<SEC-DOCUMENT>0001922140-24-000001.txt : 20240131
<SEC-HEADER>0001922140-24-000001.hdr.sgml : 20240131
<ACCEPTANCE-DATETIME>20240131183946
ACCESSION NUMBER:		0001922140-24-000001
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20240130
FILED AS OF DATE:		20240131
DATE AS OF CHANGE:		20240131

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			Ma-Weaver Jacob
		CENTRAL INDEX KEY:			0001922140
		ORGANIZATION NAME:           	

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-22873
		FILM NUMBER:		24584399

	MAIL ADDRESS:	
		STREET 1:		2261 MARKET STREET
		STREET 2:		#4307
		CITY:			SAN FRANCISCO
		STATE:			CA
		ZIP:			94114

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			ARCA biopharma, Inc.
		CENTRAL INDEX KEY:			0000907654
		STANDARD INDUSTRIAL CLASSIFICATION:	IN VITRO & IN VIVO DIAGNOSTIC SUBSTANCES [2835]
		ORGANIZATION NAME:           	03 Life Sciences
		IRS NUMBER:				363855489
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		10170 CHURCH RANCH WAY
		STREET 2:		SUITE 100
		CITY:			WESTMINSTER
		STATE:			CO
		ZIP:			80021
		BUSINESS PHONE:		7209402200

	MAIL ADDRESS:	
		STREET 1:		10170 CHURCH RANCH WAY
		STREET 2:		SUITE 100
		CITY:			WESTMINSTER
		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>primary_doc.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0508</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2024-01-30</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001922140</rptOwnerCik>
            <rptOwnerName>Ma-Weaver Jacob</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>2261 MARKET STREET</rptOwnerStreet1>
            <rptOwnerStreet2>#4307</rptOwnerStreet2>
            <rptOwnerCity>SAN FRANCISCO</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>94114</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>1</isOther>
            <otherText>See footnote 1</otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <aff10b5One>0</aff10b5One>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Stock option (right to buy)</value>
                <footnoteId id="F1"/>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>1.64</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2024-01-30</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>6000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F2"/>
            </exerciseDate>
            <expirationDate>
                <value>2034-01-30</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>6000</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>6000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">This Form 4 is filed by Jacob Ma-Weaver. Mr. Ma-Weaver, Funicular Funds, LP, and Cable Car Capital LLC may be deemed to be members of a Section 13(d) group that may be deemed to collectively beneficially own more than 10% of the Issuer's outstanding shares of Common Stock. Each of the Reporting Persons disclaims beneficial ownership of the securities reported herein except to the extent of his or its pecuniary interest therein.</footnote>
        <footnote id="F2">Grant to the Reporting Person of a stock option under the 2020 Equity Incentive Plan, vesting in 12 equal monthly installments beginning as of January 30, 2024, subject to the Reporting Person continuing to provide Continuous Service (as defined in the 2020 Equity Incentive Plan) through such date. If the Reporting Person's service as a director of the Issuer terminates in connection with or at any time following a change in control (for whatever reason), then any unexpired options that remain unvested shall become fully vested.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>Jacob Ma-Weaver</signatureName>
        <signatureDate>2024-01-31</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
