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Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
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 TWSM7vrzLADbmYQaionwg5sDW3P6oaM5D3tdezXMm7z1T+B+twIDAQAB
MIC-Info: RSA-MD5,RSA,
 AXJc7uRzvNGqOJHx+ogiq3RLWBJnQyYldLkQu4BAY6Ew6niaI/bDP9Ne6v93CWSs
 oJkRAbJ2oHR4lRPZtWw9Fg==

<SEC-DOCUMENT>0001123292-09-000263.txt : 20090303
<SEC-HEADER>0001123292-09-000263.hdr.sgml : 20090303
<ACCEPTANCE-DATETIME>20090303152419
ACCESSION NUMBER:		0001123292-09-000263
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20090227
FILED AS OF DATE:		20090303
DATE AS OF CHANGE:		20090303

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			FREYTAG J WILLIAM
		CENTRAL INDEX KEY:			0001266124

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-22873
		FILM NUMBER:		09651425

	BUSINESS ADDRESS:	
		STREET 1:		7575 WEST 103RD AVENUE
		STREET 2:		SUITE 102
		CITY:			WESTMINSTER
		STATE:			CO
		ZIP:			80021
		BUSINESS PHONE:		3034106666

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
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>edgar.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2009-02-27</periodOfReport>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001266124</rptOwnerCik>
            <rptOwnerName>FREYTAG J WILLIAM</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>7169 WATERFORD COURT</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>NIWOT</rptOwnerCity>
            <rptOwnerState>CO</rptOwnerState>
            <rptOwnerZipCode>80503</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Option to Purchase Common Stock</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>5.29</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2009-02-27</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>7500</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F1"/>
            </exerciseDate>
            <expirationDate>
                <value>2019-02-27</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>7500</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>7500</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">The options vest ratably on a monthly basis over a two year period; full acceleration upon change in control and termination of service.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Patrick Wheeler, attorney in fact</signatureName>
        <signatureDate>2009-03-03</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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