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Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
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<SEC-DOCUMENT>0001123292-09-000128.txt : 20090205
<SEC-HEADER>0001123292-09-000128.hdr.sgml : 20090205
<ACCEPTANCE-DATETIME>20090205160428
ACCESSION NUMBER:		0001123292-09-000128
CONFORMED SUBMISSION TYPE:	3
PUBLIC DOCUMENT COUNT:		2
CONFORMED PERIOD OF REPORT:	20090127
FILED AS OF DATE:		20090205
DATE AS OF CHANGE:		20090205

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			Skyline Venture Partners Qualified Purchaser Fund IV L P
		CENTRAL INDEX KEY:			0001324617

	FILING VALUES:
		FORM TYPE:		3
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-22873
		FILM NUMBER:		09573091

	BUSINESS ADDRESS:	
		STREET 1:		125 UNIVERSITY AVE
		CITY:			PALO ALTO
		STATE:			CA
		ZIP:			94301

	MAIL ADDRESS:	
		STREET 1:		125 UNIVERSITY AVE
		CITY:			PALO ALTO
		STATE:			CA
		ZIP:			94301

ISSUER:		

	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

	BUSINESS ADDRESS:	
		STREET 1:		8001 ARISTA PLACE
		STREET 2:		SUITE 200
		CITY:			BROOMFIELD
		STATE:			CO
		ZIP:			80021
		BUSINESS PHONE:		720-940-2200

	MAIL ADDRESS:	
		STREET 1:		8001 ARISTA PLACE
		STREET 2:		SUITE 200
		CITY:			BROOMFIELD
		STATE:			CO
		ZIP:			80021

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

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	HYSEQ INC
		DATE OF NAME CHANGE:	19970610
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<SEQUENCE>1
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<DESCRIPTION>PRIMARY DOCUMENT
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<ownershipDocument>

    <schemaVersion>X0203</schemaVersion>

    <documentType>3</documentType>

    <periodOfReport>2009-01-27</periodOfReport>

    <noSecuritiesOwned>0</noSecuritiesOwned>

    <issuer>
        <issuerCik>0000907654</issuerCik>
        <issuerName>ARCA biopharma, Inc.</issuerName>
        <issuerTradingSymbol>ABIO</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001324617</rptOwnerCik>
            <rptOwnerName>Skyline Venture Partners Qualified Purchaser Fund IV L P</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1></rptOwnerStreet1>
            <rptOwnerStreet2>525 UNIVERSITY AVENUE, STE 520</rptOwnerStreet2>
            <rptOwnerCity>PALO ALTO</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>94301</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>877583</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeHolding>
            <securityTitle>
                <value>Warrant to Purchase Common Stock</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>9.7406</value>
            </conversionOrExercisePrice>
            <exerciseDate>
                <footnoteId id="F1"/>
            </exerciseDate>
            <expirationDate>
                <value>2013-10-10</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>37486</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeHolding>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">This warrant is immediately exercisable.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Patrick Wheeler, attorney in fact</signatureName>
        <signatureDate>2009-02-05</signatureDate>
    </ownerSignature>
</ownershipDocument>
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<p style=' margin-bottom:0pt; margin-top:0pt;text-align:center;'><b><small>ARCA</small> <small>BIOPHARMA,</small> <small>INC.</small></b></p>

<p style=' margin-bottom:0pt; margin-top:0pt;text-align:center;'><font size=2>&nbsp;</font></p>

<p style=' margin-bottom:12pt; margin-top:0pt;text-align:center;'><B><font SIZE=2>POWER OF ATTORNEY</font></B></p>

<p style=' margin-bottom:12pt; margin-top:0pt; text-indent:0.5in;text-align:left;'><font size=2>Know all by these presents, that the undersigned hereby constitutes and appoints each of Christopher Ozeroff, Patrick Wheeler, Brian Selby and Paula Evans, signing singly, and with full power of substitution, the undersigned&#146;s true and lawful attorney-in-fact to:</font></p>

<p style=' margin-bottom:12pt; margin-top:0pt; text-indent:0.54in;text-align:left;'><font size=2> (1)&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;execute and file for and on behalf of the undersigned, in the undersigned&#146;s name, place and stead, in any and all capacities, all Forms 3, 4 and 5 (including any amendments thereto) that the undersigned may be required to file with the United States Securities and Exchange Commission as a result of the undersigned&#146;s ownership of or transactions in securities of ARCA biopharma, Inc. (the &#147;</font><u><font size=2>Company</font></u><font size=2>&#148;);</font></p>

<p style=' margin-bottom:12pt; margin-top:0pt; text-indent:0.54in;text-align:left;'><font size=2> (2)&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;do and perform any and all acts for and on behalf of the undersigned which may be necessary or desirable to complete and execute any such Form 3, 4 or 5 and timely file any such form with the United States Securities and Exchange Commission and any stock exchange or similar authority; and</font></p>

<p style=' margin-bottom:12pt; margin-top:0pt; text-indent:0.54in;text-align:left;'><font size=2> (3)&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;take any other action of any type whatsoever in connection with the foregoing which, in the opinion of such attorney-in-fact, may be of benefit to, and in the best interest of, or legally required by, the undersigned.</font></p>

<p style=' margin-bottom:12pt; margin-top:0pt; text-indent:0.5in;text-align:left;'><font size=2>The undersigned hereby grants to each such attorney-in-fact full power and authority to do and perform any and every act and thing whatsoever requisite, necessary, or proper to be done in the exercise of any of the rights and powers herein granted, as fully to all intents and purposes as the undersigned might or could do if personally present, with full power of substitution or revocation, hereby ratifying and confirming all that such attorney-in-fact, or such attorney-in-fact&#146;s substitute or substitutes, shall lawfully do or cause to be done by virtue of this power of attorney and the rights and powers herein granted.  The undersigned acknowledges that the foregoing attorneys-in-fact, in serving in such capacity at the request of the undersigned, are not assuming, nor is the Company assuming, any of the undersigned&#146;s responsibilities to comply with Section 16 of the Securities
Exchange Act of 1934.</font></p>

<p style=' margin-bottom:12pt; margin-top:0pt; text-indent:0.5in;text-align:left;'><font size=2>This Power of Attorney shall remain in full force and effect until the undersigned is no longer required to file Forms 3, 4 and 5 with respect to the undersigned&#146;s holdings of and transactions in securities issued by the Company, unless earlier revoked by the undersigned in a signed writing delivered to the foregoing attorneys-in-fact.</font></p>


<p style=' margin-bottom:0pt; margin-top:0pt;text-align:left;'>
<font size=2>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;IN WITNESS WHEREOF, the undersigned has caused this Power of Attorney to be executed as of January 27, 2009.</font></p>

<p style=' margin-bottom:0pt; margin-top:0pt;text-align:left;'><font size=2>&nbsp;</font></p>

<p style=' margin-bottom:0pt; margin-top:0pt; margin-left:3.5in;text-align:left;'><b><font size=2>Skyline Venture Partners Qualified Purchaser Fund IV, L.P.</font></b></p>

<p style=' margin-bottom:0pt; margin-top:0pt; margin-left:3.5in;text-align:left;'><font size=2>&nbsp;</font></p>

<p style=' margin-bottom:0pt; margin-top:0pt; margin-left:3.5in;text-align:left;'><font size=2>By: Skyline Venture Management IV, LLC</font></p>

<p style=' margin-bottom:0pt; margin-top:0pt; margin-left:3.5in;text-align:left;'><font size=2>Its General Partner</font></p>

<p style=' margin-bottom:0pt; margin-top:0pt; margin-left:3.5in;text-align:left;'><font size=2>&nbsp;</font></p>

<p style=' margin-bottom:0pt; margin-top:0pt; margin-left:3.5in;text-align:left;'><font size=2>By: </font><u><font size=2>/s/ John G. Freund </font></u><font size=2>&nbsp;</font></p>


<div align=left>

<table border="0" cellspacing=0 cellpadding=0 width="612" style='border-collapse:collapse'>
    <tr >
        <td width="364" nowrap valign=top >
            <p style='margin-left:0pt;text-indent:0pt;text-align:left;margin-top:0pt;margin-bottom:0pt'><font size=1>&nbsp;</font></p> </td>
        <td width="248" nowrap valign=top >
            <p style='margin-left:0pt;text-indent:0pt;text-align:left;margin-top:0pt;margin-bottom:0pt'><font size=2>John G. Freund, Managing Director</font></p> </td> </tr></table>
</div>

<p style=' margin-bottom:0pt; margin-top:0pt;text-align:left;'><font size=2>&nbsp;</font></p>

<p style=' margin-bottom:0pt; margin-top:0pt;text-align:left;'><font size=2>&nbsp;</font></p>

<p style=' margin-bottom:0pt; margin-top:0pt;text-align:left;'><font size=2>&nbsp;</font></p>
<!-- EEDocs PBStart-->
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<p style=' margin-bottom:0pt; margin-top:0pt;text-align:left;'><font size=2>&nbsp;</font></p>



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