    <SEC-DOCUMENT>0001564590-21-019820-index.html : 20210421
    <SEC-HEADER>0001564590-21-019820.hdr.sgml : 20210421
    <ACCEPTANCE-DATETIME>20210421161246
    ACCESSION NUMBER:		0001564590-21-019820
    CONFORMED SUBMISSION TYPE:	DEFA14A
    PUBLIC DOCUMENT COUNT:		3
    FILED AS OF DATE:		20210421
    DATE AS OF CHANGE:		20210421

    FILER:

    	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:		DEFA14A
    		SEC ACT:		1934 Act
    		SEC FILE NUMBER:	000-22873
    		FILM NUMBER:		21841678

    	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>DEFA14A
    <SEQUENCE>1
    <FILENAME>abio-defa14a_20210415.htm
    <DESCRIPTION>DEFA14A
    <TEXT>
    Document 1 - file: abio-defa14a_20210415.htm

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>2
    <FILENAME>g1tmjs5mu2js000002.jpg
    <DESCRIPTION>GRAPHIC
    <TEXT>
    Document 2 - file: g1tmjs5mu2js000002.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>3
    <FILENAME>g1tmjs5mu2js000001.jpg
    <DESCRIPTION>GRAPHIC
    <TEXT>
    Document 3 - file: g1tmjs5mu2js000001.jpg

    </DOCUMENT>
    </SEC-DOCUMENT>