<SEC-DOCUMENT>0001144204-15-039125.txt : 20150625
<SEC-HEADER>0001144204-15-039125.hdr.sgml : 20150625
<ACCEPTANCE-DATETIME>20150625164101
ACCESSION NUMBER:		0001144204-15-039125
CONFORMED SUBMISSION TYPE:	SC 13G
PUBLIC DOCUMENT COUNT:		1
FILED AS OF DATE:		20150625
DATE AS OF CHANGE:		20150625
GROUP MEMBERS:		PETER KOLCHINSKY
GROUP MEMBERS:		RA CAPITAL HEALTHCARE FUND, L.P.

SUBJECT COMPANY:	

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			ARCA biopharma, Inc.
		CENTRAL INDEX KEY:			0000907654
		STANDARD INDUSTRIAL CLASSIFICATION:	IN VITRO & IN VIVO DIAGNOSTIC SUBSTANCES [2835]
		IRS NUMBER:				363855489
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	FILING VALUES:
		FORM TYPE:		SC 13G
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	005-51477
		FILM NUMBER:		15952216

	BUSINESS ADDRESS:	
		STREET 1:		11080 CIRCLEPOINT ROAD
		STREET 2:		SUITE 140
		CITY:			WESTMINSTER
		STATE:			CO
		ZIP:			80020
		BUSINESS PHONE:		720-940-2200

	MAIL ADDRESS:	
		STREET 1:		11080 CIRCLEPOINT ROAD
		STREET 2:		SUITE 140
		CITY:			WESTMINSTER
		STATE:			CO
		ZIP:			80020

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	NUVELO INC
		DATE OF NAME CHANGE:	20030203

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	HYSEQ INC
		DATE OF NAME CHANGE:	19970610

FILED BY:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			RA CAPITAL MANAGEMENT, LLC
		CENTRAL INDEX KEY:			0001346824
		IRS NUMBER:				830406777
		STATE OF INCORPORATION:			MA
		FISCAL YEAR END:			1231

	FILING VALUES:
		FORM TYPE:		SC 13G

	BUSINESS ADDRESS:	
		STREET 1:		20 PARK PLAZA, SUITE 1200
		CITY:			BOSTON
		STATE:			MA
		ZIP:			02116
		BUSINESS PHONE:		617-778-2500

	MAIL ADDRESS:	
		STREET 1:		20 PARK PLAZA, SUITE 1200
		CITY:			BOSTON
		STATE:			MA
		ZIP:			02116
</SEC-HEADER>
<DOCUMENT>
<TYPE>SC 13G
<SEQUENCE>1
<FILENAME>v414161_sc13g.htm
<DESCRIPTION>SC 13G
<TEXT>
<HTML>
<HEAD>
     <TITLE></TITLE>
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<BODY STYLE="font: 10pt Times New Roman, Times, Serif">

<P STYLE="margin: 0">&nbsp;&nbsp;</P>

<P STYLE="font: bold 10pt Times New Roman, Times, Serif; margin-top: 0pt; margin-bottom: 0pt; text-align: center">UNITED STATES<BR>
SECURITIES AND EXCHANGE COMMISSION<BR>
Washington, D.C. 20549</P>

<P STYLE="font: bold 10pt Times New Roman, Times, Serif; margin-top: 0pt; margin-bottom: 0pt; text-align: center">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; text-align: center; margin-bottom: 0pt">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; margin-bottom: 0pt; text-align: center"><B>SCHEDULE 13G</B></P>

<P STYLE="font: bold 10pt Times New Roman, Times, Serif; margin-top: 0pt; margin-bottom: 0pt; text-align: center">Under the Securities Exchange Act of
1934</P>

<P STYLE="font: bold 10pt Times New Roman, Times, Serif; margin-top: 0pt; margin-bottom: 0pt; text-align: center">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; margin-bottom: 0pt; text-align: center"><B>(Amendment No.__)*</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; margin-bottom: 0pt; text-align: center">&nbsp;</P>

<P STYLE="font: bold 10pt Times New Roman, Times, Serif; margin-top: 0pt; margin-bottom: 0pt; text-align: center"><BR>
ARCA biopharma, Inc.</P>

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<P STYLE="font: bold 10pt Times New Roman, Times, Serif; margin-top: 0pt; margin-bottom: 0pt; text-align: center"></P>



<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; margin-bottom: 0pt; text-align: center">(Name of Issuer)</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; margin-bottom: 0pt; text-align: center">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; margin-bottom: 0pt; text-align: center"><B>Common Stock, par value $0.001 per share</B></P>

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<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; margin-bottom: 0pt; text-align: center"></P>



<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; margin-bottom: 0pt; text-align: center">(Title of Class of Securities)</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; margin-bottom: 0pt; text-align: center">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; margin-bottom: 0pt; text-align: center"><B>00211Y209</B></P>

<!-- Field: Rule-Page --><DIV STYLE="text-align: center; margin-top: 3pt; margin-bottom: 3pt"><DIV STYLE="font-size: 1pt; border-top: Black 1pt solid; width: 100%; text-align: center">&nbsp;</DIV></DIV><!-- Field: /Rule-Page -->

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; margin-bottom: 0pt; text-align: center"></P>



<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; margin-bottom: 0pt; text-align: center">(CUSIP Number)</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; margin-bottom: 0pt; text-align: center">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; margin-bottom: 0pt; text-align: center"><B>June 16, 2015</B></P>

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<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; margin-bottom: 0pt; text-align: center"></P>



<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; margin-bottom: 0pt; text-align: center">(Date of Event Which Requires Filing of
this Statement)</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">Check the appropriate box to designate the rule pursuant to
which this Schedule is filed:</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<TABLE CELLSPACING="0" CELLPADDING="0" STYLE="width: 100%; font: 10pt Times New Roman, Times, Serif">
<tr>
    <TD STYLE="width: 3%">&nbsp;</TD>
    <TD STYLE="padding: 0; text-indent: 0; width: 3%"><FONT STYLE="font-family: Wingdings">&#168;</FONT></td>
    <TD STYLE="padding: 0; text-indent: 0; width: 94%">Rule 13d-1(b)</td></tr>
<tr>
    <TD>&nbsp;</TD>
    <TD STYLE="padding: 0; text-indent: 0"><FONT STYLE="font-family: Wingdings">&#120;</FONT></td>
    <TD STYLE="padding: 0; text-indent: 0">Rule 13d-1(c)</td></tr>
<tr>
    <TD>&nbsp;</TD>
    <TD STYLE="padding: 0; text-indent: 0"><FONT STYLE="font-family: Wingdings">&#168;</FONT></td>
    <TD STYLE="padding: 0; text-indent: 0">Rule 13d-1(d)</td></tr>
</table>
<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify">*The remainder of this cover page shall
be filled out for a reporting person&rsquo;s initial filing on this form with respect to the subject class of securities, and for
any subsequent amendment containing information which would alter the disclosures provided in a prior cover page.</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify">The information required in the remainder
of this cover page shall not be deemed to be &ldquo;filed&rdquo; for the purpose of Section 18 of the Securities Exchange Act of
1934 (&ldquo;<B><I>Act</I></B>&rdquo;) or otherwise subject to the liabilities of that section of the Act but shall be subject
to all other provisions of the Act (however, see the Notes).</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify"></P>

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    <DIV STYLE="page-break-before: always; margin-top: 6pt; margin-bottom: 12pt"><TABLE CELLPADDING="0" CELLSPACING="0" STYLE="width: 100%"><TR><TD STYLE="text-align: center; width: 100%">&nbsp;</TD></TR></TABLE></DIV>
    <!-- Field: /Page -->

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify">&nbsp;</P>




<table cellspacing="0" cellpadding="0" style="font: 10pt Times New Roman, Times, Serif; width: 100%">
<tr>
    <TD COLSPAN="5" STYLE="padding: 0; font-size: 10pt; text-indent: 0"><font style="font-size: 10pt">CUSIP No. </font><b>00211Y209</b></td>
    <TD STYLE="padding: 0; font-size: 12pt; text-align: center; text-indent: 0"><font style="font-size: 12pt"><b>13G</b></font></td>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0">&nbsp;</td></tr>
<tr>
    <TD COLSPAN="7" STYLE="padding: 0; text-indent: 0">



        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
<tr>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid">&nbsp;</td>
    <TD STYLE="vertical-align: top; padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid"><font style="font-size: 10pt">1.</font></td>
    <TD COLSPAN="5" STYLE="padding: 0; text-indent: 0; border-top: Black 1pt solid">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">Names of Reporting Persons.<br>
        I.R.S. Identification Nos. of above persons (entities only).</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in"><b>RA Capital Management, LLC&#9;</b></P></td></tr>
<tr>
    <TD COLSPAN="7" STYLE="padding: 0; text-indent: 0">


        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
<tr>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid">&nbsp;</td>
    <TD STYLE="vertical-align: top; padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid"><font style="font-size: 10pt">2. </font></td>
    <TD COLSPAN="5" STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid"><font style="font-size: 10pt">Check the Appropriate Box if a Member of a Group (See Instructions)</font></td></tr>
<tr>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0">&nbsp;</td>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0">&nbsp;</td>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0"><font style="font-size: 10pt">(a)</font></td>
    <TD COLSPAN="4" STYLE="padding: 0; font-size: 10pt; text-indent: 0"><FONT STYLE="font-family: Wingdings">&#168;</FONT></td></tr>
<TR>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0">&nbsp;</TD>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0">&nbsp;</TD>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0">&nbsp;</TD>
    <TD COLSPAN="4" STYLE="padding: 0; font-size: 10pt; text-indent: 0">&nbsp;</TD></TR>
<tr>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0">&nbsp;</td>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0">&nbsp;</td>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0"><font style="font-size: 10pt">(b)</font></td>
    <TD COLSPAN="4" STYLE="padding: 0; font-size: 10pt; text-indent: 0"><FONT STYLE="font-family: Wingdings">&#168;</FONT></td></tr>
<tr>
    <TD COLSPAN="7" STYLE="padding: 0; text-indent: 0">


        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
<tr>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid">&nbsp;</td>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid"><font style="font-size: 10pt">3.</font></td>
    <TD COLSPAN="5" STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid"><font style="font-size: 10pt">SEC Use Only </font></td></tr>
<tr>
    <TD COLSPAN="7" STYLE="padding: 0; text-indent: 0">


        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
<tr>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid">&nbsp;</td>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid"><font style="font-size: 10pt">4.</font></td>
    <TD COLSPAN="5" STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid"><font style="font-size: 10pt">Citizenship or Place of Organization&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</font>&nbsp;<font style="font-size: 10pt"><b>Massachusetts</b></font></td></tr>
<tr>
    <TD COLSPAN="7" STYLE="padding: 0; text-indent: 0; border-bottom: Black 1pt solid">


        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
<tr>
    <TD COLSPAN="3" ROWSPAN="7" STYLE="padding: 0; font-size: 10pt; text-indent: 0"><font style="font-size: 10pt">Number of</font><br>
<font style="font-size: 10pt">Shares</font><br>
<font style="font-size: 10pt">Beneficially</font><br>
<font style="font-size: 10pt">Owned by</font><br>
<font style="font-size: 10pt">Each Reporting</font><br>
<font style="font-size: 10pt">Person With</font></td>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0"><font style="font-size: 10pt">5.</font></td>
    <TD COLSPAN="3" STYLE="font-size: 10pt; padding: 0; text-indent: 0"><font style="font-size: 10pt">Sole Voting Power&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<b>0 shares</b></font></td></tr>
<tr>
    <TD COLSPAN="4" STYLE="padding: 0; text-indent: 0">


        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
<tr>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid"><font style="font-size: 10pt">6.</font></td>
    <TD COLSPAN="3" STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid"><font style="font-size: 10pt">Shared Voting Power&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<b>5,678,592 shares</b></font></td></tr>
<tr>
    <TD COLSPAN="4" STYLE="padding: 0; text-indent: 0">


        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
<tr>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid"><font style="font-size: 10pt">7.</font></td>
    <TD COLSPAN="3" STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid"><font style="font-size: 10pt">Sole Dispositive Power&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<b>0 shares</b></font></td></tr>
<tr>
    <TD COLSPAN="4" STYLE="padding: 0; text-indent: 0">


        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
<tr>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid"><font style="font-size: 10pt">8.</font></td>
    <TD COLSPAN="3" STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid"><font style="font-size: 10pt">Shared Dispositive Power&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<b>5,678,592 shares</b></font></td></tr>
<tr>
    <TD COLSPAN="7" STYLE="padding: 0; text-indent: 0">


        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
<tr>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid">&nbsp;</td>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid; text-align: left; vertical-align: top"><font style="font-size: 10pt">9.</font></td>
    <TD COLSPAN="5" STYLE="padding: 0; text-indent: 0; border-top: Black 1pt solid">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">Aggregate Amount Beneficially Owned by Each Reporting Person</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in"><b>5,678,592 shares</b></P></td></tr>
<tr>
    <TD COLSPAN="7" STYLE="padding: 0; text-indent: 0">


        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
<tr>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid">&nbsp;</td>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid"><font style="font-size: 10pt">10.</font></td>
    <TD COLSPAN="5" STYLE="padding: 0; text-indent: 0; border-top: Black 1pt solid">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"><FONT STYLE="font-size: 10pt">Check if the Aggregate
Amount in Row (9) Excludes Certain Shares (See Instructions)&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; <FONT STYLE="font-family: Wingdings">&#168;
</FONT></FONT></P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"></P></td></tr>
<tr>
    <TD COLSPAN="7" STYLE="padding: 0; text-indent: 0">


        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
<tr>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid">&nbsp;</td>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid; text-align: left; vertical-align: top"><font style="font-size: 10pt">11.</font></td>
    <TD COLSPAN="5" STYLE="padding: 0; text-indent: 0; border-top: Black 1pt solid">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">Percent of Class Represented by Amount in Row (9)</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in"><b>9.0%</b></P></td></tr>
<tr>
    <TD COLSPAN="7" STYLE="padding: 0; text-indent: 0">


        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
<tr>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid">&nbsp;</td>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid; text-align: left; vertical-align: top"><font style="font-size: 10pt">12.</font></td>
    <TD COLSPAN="5" STYLE="padding: 0; text-indent: 0; border-top: Black 1pt solid">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">Type of Reporting Person (See Instructions)</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in"><b>IA</b></P></td></tr>
<tr>
    <TD COLSPAN="7" STYLE="padding: 0; text-indent: 0; border-bottom: Black 1pt solid">


        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
<tr>
    <TD STYLE="width: 4%; padding: 0; text-indent: 0">&nbsp;</td>
    <TD STYLE="width: 7%; padding: 0; text-indent: 0">&nbsp;</td>
    <TD STYLE="width: 5%; padding: 0; text-indent: 0">&nbsp;</td>
    <TD STYLE="width: 4%; padding: 0; text-indent: 0">&nbsp;</td>
    <TD STYLE="width: 23%; padding: 0; text-indent: 0">&nbsp;</td>
    <TD STYLE="width: 22%; padding: 0; text-indent: 0">&nbsp;</td>
    <TD STYLE="width: 35%; padding: 0; text-indent: 0">&nbsp;</td></tr>
</table>



<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"></P>

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<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<table cellspacing="0" cellpadding="0" style="font: 10pt Times New Roman, Times, Serif; width: 100%">
<tr>
    <TD COLSPAN="5" STYLE="padding: 0; font-size: 10pt; text-indent: 0"><font style="font-size: 10pt">CUSIP No. </font><b>00211Y209</b></td>
    <TD STYLE="padding: 0; font-size: 12pt; text-align: center; text-indent: 0"><font style="font-size: 12pt"><b>13G</b></font></td>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0">&nbsp;</td></tr>
<tr>
    <TD COLSPAN="7" STYLE="padding: 0; text-indent: 0">



        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
<tr>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid">&nbsp;</td>
    <TD STYLE="vertical-align: top; padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid"><font style="font-size: 10pt">1.</font></td>
    <TD COLSPAN="5" STYLE="padding: 0; text-indent: 0; border-top: Black 1pt solid">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">Names of Reporting Persons.<br>
        I.R.S. Identification Nos. of above persons (entities only).</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in"><b>Peter Kolchinsky&#9;</b></P></td></tr>
<tr>
    <TD COLSPAN="7" STYLE="padding: 0; text-indent: 0">


        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
<tr>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid">&nbsp;</td>
    <TD STYLE="vertical-align: top; padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid"><font style="font-size: 10pt">2. </font></td>
    <TD COLSPAN="5" STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid"><font style="font-size: 10pt">Check the Appropriate Box if a Member of a Group (See Instructions)</font></td></tr>
<tr>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0">&nbsp;</td>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0">&nbsp;</td>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0"><font style="font-size: 10pt">(a)</font></td>
    <TD COLSPAN="4" STYLE="padding: 0; font-size: 10pt; text-indent: 0"><FONT STYLE="font-family: Wingdings">&#168;</FONT></td></tr>
<TR>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0">&nbsp;</TD>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0">&nbsp;</TD>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0">&nbsp;</TD>
    <TD COLSPAN="4" STYLE="padding: 0; font-size: 10pt; text-indent: 0">&nbsp;</TD></TR>
<tr>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0">&nbsp;</td>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0">&nbsp;</td>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0"><font style="font-size: 10pt">(b)</font></td>
    <TD COLSPAN="4" STYLE="padding: 0; font-size: 10pt; text-indent: 0"><FONT STYLE="font-family: Wingdings">&#168;</FONT></td></tr>
<tr>
    <TD COLSPAN="7" STYLE="padding: 0; text-indent: 0">


        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
<tr>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid">&nbsp;</td>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid"><font style="font-size: 10pt">3.</font></td>
    <TD COLSPAN="5" STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid"><font style="font-size: 10pt">SEC Use Only </font></td></tr>
<tr>
    <TD COLSPAN="7" STYLE="padding: 0; text-indent: 0">


        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
<tr>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid">&nbsp;</td>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid"><font style="font-size: 10pt">4.</font></td>
    <TD COLSPAN="5" STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid"><font style="font-size: 10pt">Citizenship or Place of Organization&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</font>&nbsp;<b>United States</b></td></tr>
<tr>
    <TD COLSPAN="7" STYLE="padding: 0; text-indent: 0; border-bottom: Black 1pt solid">


        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
<tr>
    <TD COLSPAN="3" ROWSPAN="7" STYLE="padding: 0; font-size: 10pt; text-indent: 0"><font style="font-size: 10pt">Number of</font><br>
<font style="font-size: 10pt">Shares</font><br>
<font style="font-size: 10pt">Beneficially</font><br>
<font style="font-size: 10pt">Owned by</font><br>
<font style="font-size: 10pt">Each Reporting</font><br>
<font style="font-size: 10pt">Person With</font></td>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0"><font style="font-size: 10pt">5.</font></td>
    <TD COLSPAN="3" STYLE="font-size: 10pt; padding: 0; text-indent: 0"><font style="font-size: 10pt">Sole Voting Power&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<b>0 shares</b></font></td></tr>
<tr>
    <TD COLSPAN="4" STYLE="padding: 0; text-indent: 0">


        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
<tr>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid"><font style="font-size: 10pt">6.</font></td>
    <TD COLSPAN="3" STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid"><font style="font-size: 10pt">Shared Voting Power&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<b>5,678,592 shares</b></font></td></tr>
<tr>
    <TD COLSPAN="4" STYLE="padding: 0; text-indent: 0">


        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
<tr>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid"><font style="font-size: 10pt">7.</font></td>
    <TD COLSPAN="3" STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid"><font style="font-size: 10pt">Sole Dispositive Power&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<b>0 shares</b></font></td></tr>
<tr>
    <TD COLSPAN="4" STYLE="padding: 0; text-indent: 0">


        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
<tr>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid"><font style="font-size: 10pt">8.</font></td>
    <TD COLSPAN="3" STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid"><font style="font-size: 10pt">Shared Dispositive Power&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<b>5,678,592 shares</b></font></td></tr>
<tr>
    <TD COLSPAN="7" STYLE="padding: 0; text-indent: 0">


        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
<tr>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid">&nbsp;</td>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid; text-align: left; vertical-align: top"><font style="font-size: 10pt">9.</font></td>
    <TD COLSPAN="5" STYLE="padding: 0; text-indent: 0; border-top: Black 1pt solid">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">Aggregate Amount Beneficially Owned by Each Reporting Person</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in"><b>5,678,592 shares</b></P></td></tr>
<tr>
    <TD COLSPAN="7" STYLE="padding: 0; text-indent: 0">


        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
<tr>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid">&nbsp;</td>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid"><font style="font-size: 10pt">10.</font></td>
    <TD COLSPAN="5" STYLE="padding: 0; text-indent: 0; border-top: Black 1pt solid">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"><FONT STYLE="font-size: 10pt">Check if the Aggregate
Amount in Row (9) Excludes Certain Shares (See Instructions) &nbsp;&nbsp;&nbsp;&nbsp;<FONT STYLE="font-family: Wingdings">&#168;</FONT></FONT></P></td></tr>
<tr>
    <TD COLSPAN="7" STYLE="padding: 0; text-indent: 0">


        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
<tr>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid">&nbsp;</td>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid; text-align: left; vertical-align: top"><font style="font-size: 10pt">11.</font></td>
    <TD COLSPAN="5" STYLE="padding: 0; text-indent: 0; border-top: Black 1pt solid">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">Percent of Class Represented by Amount in Row (9)</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in"><b>9.0%</b></P></td></tr>
<tr>
    <TD COLSPAN="7" STYLE="padding: 0; text-indent: 0">


        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
<tr>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid">&nbsp;</td>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid; text-align: left; vertical-align: top"><font style="font-size: 10pt">12.</font></td>
    <TD COLSPAN="5" STYLE="padding: 0; text-indent: 0; border-top: Black 1pt solid">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">Type of Reporting Person (See Instructions)</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in"><b>IN</b></P></td></tr>
<tr>
    <TD COLSPAN="7" STYLE="padding: 0; text-indent: 0; border-bottom: Black 1pt solid">


        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
<tr>
    <TD STYLE="width: 4%; padding: 0; text-indent: 0">&nbsp;</td>
    <TD STYLE="width: 7%; padding: 0; text-indent: 0">&nbsp;</td>
    <TD STYLE="width: 5%; padding: 0; text-indent: 0">&nbsp;</td>
    <TD STYLE="width: 4%; padding: 0; text-indent: 0">&nbsp;</td>
    <TD STYLE="width: 23%; padding: 0; text-indent: 0">&nbsp;</td>
    <TD STYLE="width: 22%; padding: 0; text-indent: 0">&nbsp;</td>
    <TD STYLE="width: 35%; padding: 0; text-indent: 0">&nbsp;</td></tr>
</table>
<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"><B>&nbsp;</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"></P>

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<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<table cellspacing="0" cellpadding="0" style="font: 10pt Times New Roman, Times, Serif; width: 100%">
<tr>
    <TD COLSPAN="5" STYLE="padding: 0; font-size: 10pt; text-indent: 0"><font style="font-size: 10pt">CUSIP No. </font>&nbsp;<b>00211Y209</b></td>
    <TD STYLE="padding: 0; font-size: 12pt; text-align: center; text-indent: 0"><font style="font-size: 12pt"><b>13G</b></font></td>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0">&nbsp;</td></tr>
<tr>
    <TD COLSPAN="7" STYLE="padding: 0; text-indent: 0">



        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
<tr>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid">&nbsp;</td>
    <TD STYLE="vertical-align: top; padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid"><font style="font-size: 10pt">1.</font></td>
    <TD COLSPAN="5" STYLE="padding: 0; text-indent: 0; border-top: Black 1pt solid">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">Names of Reporting Persons.<br>
        I.R.S. Identification Nos. of above persons (entities only).</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in"><b>RA Capital Healthcare Fund, L.P.&#9;</b></P></td></tr>
<tr>
    <TD COLSPAN="7" STYLE="padding: 0; text-indent: 0">


        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
<tr>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid">&nbsp;</td>
    <TD STYLE="vertical-align: top; padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid"><font style="font-size: 10pt">2. </font></td>
    <TD COLSPAN="5" STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid"><font style="font-size: 10pt">Check the Appropriate Box if a Member of a Group (See Instructions)</font></td></tr>
<tr>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0">&nbsp;</td>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0">&nbsp;</td>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0"><font style="font-size: 10pt">(a)</font></td>
    <TD COLSPAN="4" STYLE="padding: 0; font-size: 10pt; text-indent: 0"><FONT STYLE="font-family: Wingdings">&#168;</FONT></td></tr>
<TR>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0">&nbsp;</TD>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0">&nbsp;</TD>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0">&nbsp;</TD>
    <TD COLSPAN="4" STYLE="padding: 0; font-size: 10pt; text-indent: 0">&nbsp;</TD></TR>
<tr>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0">&nbsp;</td>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0">&nbsp;</td>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0"><font style="font-size: 10pt">(b)</font></td>
    <TD COLSPAN="4" STYLE="padding: 0; font-size: 10pt; text-indent: 0"><FONT STYLE="font-family: Wingdings">&#168;</FONT></td></tr>
<tr>
    <TD COLSPAN="7" STYLE="padding: 0; text-indent: 0">


        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
<tr>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid">&nbsp;</td>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid"><font style="font-size: 10pt">3.</font></td>
    <TD COLSPAN="5" STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid"><font style="font-size: 10pt">SEC Use Only </font></td></tr>
<tr>
    <TD COLSPAN="7" STYLE="padding: 0; text-indent: 0">


        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
<tr>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid">&nbsp;</td>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid"><font style="font-size: 10pt">4.</font></td>
    <TD COLSPAN="5" STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid"><font style="font-size: 10pt">Citizenship or Place of Organization&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</font>&nbsp;<font style="font-size: 10pt"><b>Delaware</b></font></td></tr>
<tr>
    <TD COLSPAN="7" STYLE="padding: 0; text-indent: 0; border-bottom: Black 1pt solid">


        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
<tr>
    <TD COLSPAN="3" ROWSPAN="7" STYLE="padding: 0; font-size: 10pt; text-indent: 0"><font style="font-size: 10pt">Number of</font><br>
<font style="font-size: 10pt">Shares</font><br>
<font style="font-size: 10pt">Beneficially</font><br>
<font style="font-size: 10pt">Owned by</font><br>
<font style="font-size: 10pt">Each Reporting</font><br>
<font style="font-size: 10pt">Person With</font></td>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0"><font style="font-size: 10pt">5.</font></td>
    <TD COLSPAN="3" STYLE="font-size: 10pt; padding: 0; text-indent: 0"><font style="font-size: 10pt">Sole Voting Power&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<b>0 shares</b></font></td></tr>
<tr>
    <TD COLSPAN="4" STYLE="padding: 0; text-indent: 0">


        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
<tr>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid"><font style="font-size: 10pt">6.</font></td>
    <TD COLSPAN="3" STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid"><font style="font-size: 10pt">Shared Voting Power&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<b>&nbsp;4,673,481 shares</b></font></td></tr>
<tr>
    <TD COLSPAN="4" STYLE="padding: 0; text-indent: 0">


        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
<tr>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid"><font style="font-size: 10pt">7.</font></td>
    <TD COLSPAN="3" STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid"><font style="font-size: 10pt">Sole Dispositive Power&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<b>0 shares</b></font></td></tr>
<tr>
    <TD COLSPAN="4" STYLE="padding: 0; text-indent: 0">


        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
<tr>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid"><font style="font-size: 10pt">8.</font></td>
    <TD COLSPAN="3" STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid"><font style="font-size: 10pt">Shared Dispositive Power&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<b>4,673,481 shares</b></font></td></tr>
<tr>
    <TD COLSPAN="7" STYLE="padding: 0; text-indent: 0">


        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
<tr>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid">&nbsp;</td>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid; text-align: left; vertical-align: top"><font style="font-size: 10pt">9.</font></td>
    <TD COLSPAN="5" STYLE="padding: 0; text-indent: 0; border-top: Black 1pt solid">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">Aggregate Amount Beneficially Owned by Each Reporting Person</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in"><b>4,673,481 shares</b></P></td></tr>
<tr>
    <TD COLSPAN="7" STYLE="padding: 0; text-indent: 0">


        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
<tr>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid">&nbsp;</td>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid"><font style="font-size: 10pt">10.</font></td>
    <TD COLSPAN="5" STYLE="padding: 0; text-indent: 0; border-top: Black 1pt solid">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"><FONT STYLE="font-size: 10pt">Check if the Aggregate
Amount in Row (9) Excludes Certain Shares (See Instructions)&nbsp;&nbsp;&nbsp;&nbsp; <FONT STYLE="font-family: Wingdings">&#168;</FONT></FONT></P></td></tr>
<tr>
    <TD COLSPAN="7" STYLE="padding: 0; text-indent: 0">


        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
<tr>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid">&nbsp;</td>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid; text-align: left; vertical-align: top"><font style="font-size: 10pt">11.</font></td>
    <TD COLSPAN="5" STYLE="padding: 0; text-indent: 0; border-top: Black 1pt solid">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">Percent of Class Represented by Amount in Row (9)</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in"><b>7.4%</b></P></td></tr>
<tr>
    <TD COLSPAN="7" STYLE="padding: 0; text-indent: 0">


        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
<tr>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid">&nbsp;</td>
    <TD STYLE="padding: 0; font-size: 10pt; text-indent: 0; border-top: Black 1pt solid; text-align: left; vertical-align: top"><font style="font-size: 10pt">12.</font></td>
    <TD COLSPAN="5" STYLE="padding: 0; text-indent: 0; border-top: Black 1pt solid">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">Type of Reporting Person (See Instructions)</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in"><b>PN (Limited Partnership)</b></P></td></tr>
<tr>
    <TD COLSPAN="7" STYLE="padding: 0; text-indent: 0; border-bottom: Black 1pt solid">


        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></td></tr>
<tr>
    <TD STYLE="width: 4%; padding: 0; text-indent: 0">&nbsp;</td>
    <TD STYLE="width: 7%; padding: 0; text-indent: 0">&nbsp;</td>
    <TD STYLE="width: 5%; padding: 0; text-indent: 0">&nbsp;</td>
    <TD STYLE="width: 4%; padding: 0; text-indent: 0">&nbsp;</td>
    <TD STYLE="width: 23%; padding: 0; text-indent: 0">&nbsp;</td>
    <TD STYLE="width: 22%; padding: 0; text-indent: 0">&nbsp;</td>
    <TD STYLE="width: 35%; padding: 0; text-indent: 0">&nbsp;</td></tr>
</table>
<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"><B>&nbsp;</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"></P>

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<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"><FONT STYLE="font-size: 10pt">CUSIP No. </FONT><B>00211Y209</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>




<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"><B>Item 1.</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify">(a)&#9;<B>Name of Issuer:</B> ARCA biopharma,
Inc. (the &ldquo;Issuer&rdquo;).</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify">(b)&#9;<B>Address of the Issuer&rsquo;s
Principal Executive Offices:</B> 11080 CirclePoint Road, Suite 140, Westminster, CO 80020.</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify"><B>Item 2.&#9;</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify; text-indent: 0in">(a)&#9;<B>Name of Person
Filing: </B> This joint statement on Schedule 13G is being filed by Peter Kolchinsky, RA Capital Management, LLC (&ldquo;Capital&rdquo;),
and RA Capital Healthcare Fund, L.P. (the &ldquo;Fund&rdquo;). Mr. Kolchinsky, Capital and the Fund are collectively referred to
herein as the &ldquo;Reporting Persons.&rdquo;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify; text-indent: 0in">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify; text-indent: 0in">(b)&#9;<B>Address of
Principal Business Office:</B> The principal business office of the Reporting Persons is c/o RA Capital Management, LLC, 20 Park
Plaza, Suite 1200, Boston, MA 02116.</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify; text-indent: 0in">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify; text-indent: 0in">(c) &#9;<B>Citizenship:</B>
Capital is a Massachusetts limited liability company. The Fund is a Delaware limited partnership. Mr. Kolchinsky is a United States
citizen.</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify; text-indent: 0in">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify; text-indent: 0in">(d)&#9;<B>Title and Class
of Securities: </B>Common stock (&ldquo;Common Stock&rdquo;).</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify; text-indent: 0in">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify; text-indent: 0in">(e)&#9;<B>CUSIP Number:
</B>00211Y209</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify; text-indent: 0in">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify"><B>Item 3.&#9;If this statement is filed
pursuant to &sect;&sect;240.13d-1(b) or 240.13d-2(b) or (c), check whether the person filing is a:</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify">Not applicable.</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify"><B>Item 4. &#9;Ownership:</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify">Provide the following information regarding
the aggregate number and percentage of the class of securities of the issuer identified in Item 1.</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify"></P>

<TABLE CELLSPACING="0" CELLPADDING="0" STYLE="font: 10pt Times New Roman, Times, Serif; width: 100%; border-collapse: collapse">
<TR STYLE="vertical-align: top">
    <TD><FONT STYLE="font: 10pt Times New Roman, Times, Serif">(a)</FONT></TD>
    <TD><FONT STYLE="font: 10pt Times New Roman, Times, Serif">Amount Beneficially Owned:**</FONT></TD></TR>
<TR STYLE="vertical-align: top">
    <TD>&nbsp;</TD>
    <TD>&nbsp;</TD></TR>
<TR STYLE="vertical-align: top">
    <TD>&nbsp;</TD>
    <TD>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in">RA Capital Management, LLC &ndash; 5,678,592
        shares</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in">Peter Kolchinsky &ndash; 5,678,592 shares</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in">RA Capital Healthcare Fund, L.P. &ndash;
        4,673,481 shares</P></TD></TR>
<TR STYLE="vertical-align: top">
    <TD>&nbsp;</TD>
    <TD>&nbsp;</TD></TR>
<TR STYLE="vertical-align: top">
    <TD><FONT STYLE="font: 10pt Times New Roman, Times, Serif">(b)</FONT></TD>
    <TD><FONT STYLE="font: 10pt Times New Roman, Times, Serif">Percent of Class:**</FONT></TD></TR>
<TR STYLE="vertical-align: top">
    <TD>&nbsp;</TD>
    <TD>&nbsp;</TD></TR>
<TR STYLE="vertical-align: top">
    <TD>&nbsp;</TD>
    <TD>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in">RA Capital Management, LLC &ndash; 9.0%</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in">Peter Kolchinsky &ndash; 9.0%</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in">RA Capital Healthcare Fund, L.P. &ndash;
        7.4%</P></TD></TR>
</TABLE>
<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"></P>

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<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"><FONT STYLE="font-size: 10pt">CUSIP No. </FONT><B>00211Y209</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; text-align: left; margin-bottom: 0pt"></P>

<TABLE CELLSPACING="0" CELLPADDING="0" STYLE="font: 10pt Times New Roman, Times, Serif; width: 100%; border-collapse: collapse">
<TR STYLE="vertical-align: top">
    <TD><FONT STYLE="font: 10pt Times New Roman, Times, Serif">(c)</FONT></TD>
    <TD COLSPAN="2"><FONT STYLE="font: 10pt Times New Roman, Times, Serif">Number of shares as to which such person has:</FONT></TD></TR>
<TR STYLE="vertical-align: top">
    <TD>&nbsp;</TD>
    <TD COLSPAN="2">&nbsp;</TD></TR>
<TR STYLE="vertical-align: top">
    <TD>&nbsp;</TD>
    <TD><FONT STYLE="font: 10pt Times New Roman, Times, Serif">(i)</FONT></TD>
    <TD><FONT STYLE="font: 10pt Times New Roman, Times, Serif">sole power to vote or to direct the vote **</FONT></TD></TR>
<TR STYLE="vertical-align: top">
    <TD>&nbsp;</TD>
    <TD>&nbsp;</TD>
    <TD>&nbsp;</TD></TR>
<TR STYLE="vertical-align: top">
    <TD>&nbsp;</TD>
    <TD>&nbsp;</TD>
    <TD>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in">RA Capital Management, LLC - 0 shares</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in">Peter Kolchinsky - 0 shares</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in">RA Capital Healthcare Fund, L.P.
- 0 shares</P></TD></TR>
<TR STYLE="vertical-align: top">
    <TD>&nbsp;</TD>
    <TD>&nbsp;</TD>
    <TD>&nbsp;</TD></TR>
<TR STYLE="vertical-align: top">
    <TD>&nbsp;</TD>
    <TD><FONT STYLE="font: 10pt Times New Roman, Times, Serif">(ii)</FONT></TD>
    <TD><FONT STYLE="font: 10pt Times New Roman, Times, Serif">shared power to vote or to direct the vote**</FONT></TD></TR>
<TR STYLE="vertical-align: top">
    <TD>&nbsp;</TD>
    <TD>&nbsp;</TD>
    <TD>&nbsp;</TD></TR>
<TR STYLE="vertical-align: top">
    <TD>&nbsp;</TD>
    <TD>&nbsp;</TD>
    <TD>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in">RA Capital Management, LLC &ndash; 5,678,592
        shares</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in">Peter Kolchinsky &ndash; 5,678,592 shares</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in">RA Capital Healthcare Fund, L.P.
&ndash; 4,673,481 shares</P></TD></TR>
<TR STYLE="vertical-align: top">
    <TD>&nbsp;</TD>
    <TD>&nbsp;</TD>
    <TD>&nbsp;</TD></TR>
<TR STYLE="vertical-align: top">
    <TD>&nbsp;</TD>
    <TD><FONT STYLE="font: 10pt Times New Roman, Times, Serif">(iii)</FONT></TD>
    <TD><FONT STYLE="font: 10pt Times New Roman, Times, Serif">sole power to dispose or to direct the disposition of**</FONT></TD></TR>
<TR STYLE="vertical-align: top">
    <TD>&nbsp;</TD>
    <TD>&nbsp;</TD>
    <TD>&nbsp;</TD></TR>
<TR STYLE="vertical-align: top">
    <TD>&nbsp;</TD>
    <TD>&nbsp;</TD>
    <TD>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in">RA Capital Management, LLC - 0 shares</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in">Peter Kolchinsky - 0 shares</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in">RA Capital Healthcare Fund, L.P.
- 0 shares</P></TD></TR>
<TR STYLE="vertical-align: top">
    <TD>&nbsp;</TD>
    <TD>&nbsp;</TD>
    <TD>&nbsp;</TD></TR>
<TR STYLE="vertical-align: top">
    <TD>&nbsp;</TD>
    <TD><FONT STYLE="font: 10pt Times New Roman, Times, Serif">(iv)</FONT></TD>
    <TD><FONT STYLE="font: 10pt Times New Roman, Times, Serif">shared power to dispose or to direct the disposition of**</FONT></TD></TR>
<TR STYLE="vertical-align: top">
    <TD>&nbsp;</TD>
    <TD>&nbsp;</TD>
    <TD>&nbsp;</TD></TR>
<TR STYLE="vertical-align: top">
    <TD>&nbsp;</TD>
    <TD>&nbsp;</TD>
    <TD>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in">RA Capital Management, LLC &ndash; 5,678,592
        shares</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in">Peter Kolchinsky &ndash; 5,678,592 shares</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in">RA Capital Healthcare Fund, L.P.
&ndash; 4,673,481 shares</P></TD></TR>
</TABLE>
<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in">** <FONT STYLE="font-size: 10pt">RA Capital
Management, LLC (&ldquo;Capital&rdquo;) is the general partner of RA Capital Healthcare Fund, L.P. (the &ldquo;Fund&rdquo;) and
serves as investment adviser for a separately managed account (the &ldquo;Account&rdquo;). Peter Kolchinsky is the manager of Capital.
Mr. Kolchinsky, Capital and the Fund are referred to herein collectively as the &ldquo;Reporting Persons.&rdquo; As the investment
adviser to the Fund and the Account, Capital may be deemed a beneficial owner, for purposes of Section 13(d) of the Securities
Exchange Act of 1934 (the &ldquo;Act&rdquo;), of any securities of the Issuer owned by the Fund or the Account. As the manager
of Capital, Mr. Kolchinsky may be deemed a beneficial owner, for purposes of Section 13(d) of the Act, of any securities of the
Issuer beneficially owned by Capital. Capital is a registered investment adviser within the meaning of Rule 13d-1(b)(1)(ii)(E)
and Rule 16a-1(a)(v), and Mr. Kolchinsky is a parent or control person of Capital within the meaning of Rule 13d-1(b)(1)(ii)(G)
and Rule 16a-1(a)(1)(vii). Capital and Mr. Kolchinsky disclaim beneficial ownership of the securities reported in this Schedule
13G Statement (the &ldquo;Statement&rdquo;) and this Amendment other than for the purpose of determining their obligations under
Section 13(d) of the Act, and neither the filing of the Statement nor the filing of this Amendment shall not be deemed an admission
that either Capital or Mr. Kolchinsky is or was the beneficial owner of such securities for any other purpose. </FONT></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify"><B>Item 5.&#9;Ownership of Five Percent
or Less of a Class:</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify">Not applicable.</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 1in; text-align: justify; text-indent: -1in"><B>Item 6.&#9;Ownership
of More than Five Percent on Behalf of Another Person:</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 1in; text-align: justify; text-indent: -1in">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify">Not applicable.</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify"></P>

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<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify"></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"><FONT STYLE="font-size: 10pt">CUSIP No. </FONT><B>00211Y209</B></P>



<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify"><B>Item 7. &#9;Identification and Classification
of the Subsidiary Which Acquired the Security Being Reported on By the Parent Holding Company or Control Person:</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify">Not applicable.</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify"><B>Item 8.&#9;Identification and Classification
of Members of the Group:</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify">Not applicable.</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify"><B>Item 9.&#9;Notice of Dissolution of
Group:</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify">Not applicable.</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify"><B>Item 10.&#9;Certification:</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify">By signing below I hereby certify that,
to the best of my knowledge and belief, the securities referred to above were not acquired and are not held for the purpose of
or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held
in connection with or as a participant in any transaction having that purpose or effect.</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify"></P>

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<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"><FONT STYLE="font-size: 10pt">CUSIP No. </FONT><B>00211Y209</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify">&nbsp;</P>




<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center"><B>SIGNATURE</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify; text-indent: 0.5in">After reasonable inquiry
and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify; text-indent: 0.5in">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; text-align: left; margin-bottom: 0pt; margin-left: 5.75in"><FONT STYLE="text-transform: uppercase">Date: </FONT>June
25<FONT STYLE="text-transform: uppercase">, 2015</FONT></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; text-align: left; margin-bottom: 0pt; margin-left: 5.75in"><FONT STYLE="text-transform: uppercase">&nbsp;</FONT></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; text-align: left; margin-bottom: 0pt; margin-left: 5.75in"><BR>
RA CAPITAL MANAGEMENT, LLC</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; text-align: left; margin-bottom: 0pt; margin-left: 5.75in">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; text-align: left; margin-bottom: 0pt; margin-left: 5.75in">By: /s/ Rajeev Shah</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; text-align: left; margin-bottom: 0pt; margin-left: 5.75in">-------------------------------------------------</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; text-align: left; margin-bottom: 0pt; margin-left: 5.75in">Rajeev Shah</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; text-align: left; margin-bottom: 0pt; margin-left: 5.75in">Authorized Signatory</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; text-align: left; margin-bottom: 0pt; margin-left: 5.75in">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; text-align: left; margin-bottom: 0pt; margin-left: 5.75in">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; text-align: left; margin-bottom: 0pt; margin-left: 5.75in">PETER KOLCHINSKY</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; text-align: left; margin-bottom: 0pt; margin-left: 5.75in">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; text-align: left; margin-bottom: 0pt; margin-left: 5.75in">/s/ Peter Kolchinsky</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; text-align: left; margin-bottom: 0pt; margin-left: 5.75in">-------------------------------------------------</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; text-align: left; margin-bottom: 0pt; margin-left: 5.75in"><FONT STYLE="text-transform: uppercase">&nbsp;</FONT></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; text-align: left; margin-bottom: 0pt; margin-left: 5.75in"><FONT STYLE="text-transform: uppercase">&nbsp;</FONT></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; text-align: left; margin-bottom: 0pt; margin-left: 5.75in">RA CAPITAL HEALTHCARE FUND, L.P.</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; text-align: left; margin-bottom: 0pt; margin-left: 5.75in">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; text-align: left; margin-bottom: 0pt; margin-left: 5.75in">By: RA Capital Management, LLC</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; text-align: left; margin-bottom: 0pt; margin-left: 5.75in">Its: General Partner</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; text-align: left; margin-bottom: 0pt; margin-left: 5.75in">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; text-align: left; margin-bottom: 0pt; margin-left: 5.75in">By: /s/ Rajeev Shah</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; text-align: left; margin-bottom: 0pt; margin-left: 5.75in">-------------------------------------------------</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; text-align: left; margin-bottom: 0pt; margin-left: 5.75in">Rajeev Shah</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; text-align: left; margin-bottom: 0pt; margin-left: 5.75in">Authorized Signatory</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; text-align: left; margin-bottom: 0pt">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; text-align: left; margin-bottom: 0pt"></P>

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<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; text-align: left; margin-bottom: 0pt">&nbsp;</P>




<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center"><U>Exhibit 1</U></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center"><U>JOINT FILING AGREEMENT</U></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify; text-indent: 0.5in">This Joint Filing Agreement,
dated as of June 25, 2015, is by and among RA Capital Management, LLC, Peter Kolchinsky, and RA Capital Healthcare Fund, L.P. (the
foregoing are collectively referred to herein as the &ldquo;Filers&rdquo;).</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify; text-indent: 0.5in">Each of the Filers
may be required to file with the United States Securities and Exchange Commission a statement on Schedule 13G and/or 13D with respect
to Common Shares, par value $0.001 per share, of ARCA biopharma, Inc. beneficially owned by them from time to time.</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify; text-indent: 0.5in">Pursuant to and in
accordance with Rule 13(d)(1)(k) promulgated under the Securities Exchange Act of 1934, as amended, the Filers hereby agree to
file a single statement on Schedule 13G and/or 13D (and any amendments thereto) on behalf of each of such parties, and hereby further
agree to file this Joint Filing Agreement as an exhibit to such statement, as required by such rule.</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify; text-indent: 0.5in">This Joint Filing Agreement
may be terminated by any of the Filers upon one week&rsquo;s prior written notice or such lesser period of notice as the Filers
may mutually agree.</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify; text-indent: 0.5in">Executed and delivered
as of the date first above written.</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; text-align: left; margin-bottom: 0pt; margin-left: 5.75in">RA CAPITAL MANAGEMENT, LLC</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; text-align: left; margin-bottom: 0pt; margin-left: 5.75in">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; text-align: left; margin-bottom: 0pt; margin-left: 5.75in">By: /s/ Rajeev Shah</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; text-align: left; margin-bottom: 0pt; margin-left: 5.75in">-------------------------------------------------</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; text-align: left; margin-bottom: 0pt; margin-left: 5.75in">Rajeev Shah</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; text-align: left; margin-bottom: 0pt; margin-left: 5.75in">Authorized Signatory</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; text-align: left; margin-bottom: 0pt; margin-left: 5.75in">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; text-align: left; margin-bottom: 0pt; margin-left: 5.75in">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; text-align: left; margin-bottom: 0pt; margin-left: 5.75in">PETER KOLCHINSKY</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; text-align: left; margin-bottom: 0pt; margin-left: 5.75in">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; text-align: left; margin-bottom: 0pt; margin-left: 5.75in">/s/ Peter Kolchinsky</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; text-align: left; margin-bottom: 0pt; margin-left: 5.75in">-------------------------------------------------</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; text-align: left; margin-bottom: 0pt; margin-left: 5.75in"><FONT STYLE="text-transform: uppercase">&nbsp;</FONT></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; text-align: left; margin-bottom: 0pt; margin-left: 5.75in"><FONT STYLE="text-transform: uppercase">&nbsp;</FONT></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; text-align: left; margin-bottom: 0pt; margin-left: 5.75in">RA CAPITAL HEALTHCARE FUND, L.P.</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; text-align: left; margin-bottom: 0pt; margin-left: 5.75in">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; text-align: left; margin-bottom: 0pt; margin-left: 5.75in">By: RA Capital Management, LLC</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; text-align: left; margin-bottom: 0pt; margin-left: 5.75in">Its: General Partner</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; text-align: left; margin-bottom: 0pt; margin-left: 5.75in">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; text-align: left; margin-bottom: 0pt; margin-left: 5.75in">By: /s/ Rajeev Shah</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; text-align: left; margin-bottom: 0pt; margin-left: 5.75in">-------------------------------------------------</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; text-align: left; margin-bottom: 0pt; margin-left: 5.75in">Rajeev Shah</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; text-align: left; margin-bottom: 0pt; margin-left: 5.75in">Authorized Signatory</P>



<P STYLE="margin: 0"></P>

<P STYLE="margin-top: 0; text-align: left; margin-bottom: 0">&nbsp;</P>

<P STYLE="margin-top: 0; text-align: left; margin-bottom: 0"></P>

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