Ownership Submission
FORM 3
 UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

INITIAL STATEMENT OF BENEFICIAL OWNERSHIP OF SECURITIES

Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940
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(Print or Type Responses)
1. Name and Address of Reporting Person *
  VENROCK HEALTHCARE CAPITAL PARTNERS LP
 2. Date of Event Requiring Statement (Month/Day/Year)
06/16/2015		 3. Issuer Name and Ticker or Trading Symbol
ARCA biopharma, Inc. [ABIO]
(Last)
(First)
(Middle)
C/O VENROCK, 3340 HILLVIEW AVE.		 4. Relationship of Reporting Person(s) to Issuer
(Check all applicable)
_____ Director __X__ 10% Owner
_____ Officer (give title below) _____ Other (specify below)
5. If Amendment, Date Original Filed(Month/Day/Year)
(Street)

PALO ALTO, CA 94304		 6. Individual or Joint/Group Filing(Check Applicable Line)
___ Form filed by One Reporting Person
_X_ Form filed by More than One Reporting Person
(City)
(State)
(Zip)
Table I - Non-Derivative Securities Beneficially Owned
1.Title of Security
(Instr. 4)		 2. Amount of Securities Beneficially Owned
(Instr. 4)		 3. Ownership Form: Direct (D) or Indirect (I)
(Instr. 5)		 4. Nature of Indirect Beneficial Ownership
(Instr. 5)
Common Stock 10,789,324
I (1) (3)
By funds

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly. SEC 1473 (7-02)
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Table II - Derivative Securities Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security
(Instr. 4)		 2. Date Exercisable and Expiration Date
(Month/Day/Year)		 3. Title and Amount of Securities Underlying Derivative Security
(Instr. 4)		 4. Conversion or Exercise Price of Derivative Security 5. Ownership Form of Derivative Security: Direct (D) or Indirect (I)
(Instr. 5)		 6. Nature of Indirect Beneficial Ownership
(Instr. 5)
Date Exercisable Expiration Date Title Amount or Number of Shares
Warrants (right to buy) 12/13/2015 06/16/2022 Common Stock 4,315,730 $ 0.8716 I (2) (3) By funds

Reporting Owners

Reporting Owner Name / Address Relationships
Director 10% Owner Officer Other
VENROCK HEALTHCARE CAPITAL PARTNERS LP
C/O VENROCK
3340 HILLVIEW AVE.
PALO ALTO, CA 94304		     X    
Venrock Healthcare Capital Partners II, L.P.
C/O VENROCK
3340 HILLVIEW AVE.
PALO ALTO, CA 94304		     X    
VHCP Co-Investment Holdings, LLC
C/O VENROCK
3340 HILLVIEW AVE.
PALO ALTO, CA 94304		     X    
VHCP Co-Investment Holdings II, LLC
C/O VENROCK
3340 HILLVIEW AVE.
PALO ALTO, CA 94304		     X    
Koh Bong Y
C/O VENROCK
3340 HILLVIEW AVE.
PALO ALTO, CA 94304		     X    
Hove Anders D
C/O VENROCK
530 FIFTH AVENUE
NEW YORK, NY 10036		     X    
VHCP Management, LLC
C/O VENROCK
3340 HILLVIEW AVE.
PALO ALTO, CA 94304		     X    
VHCP Management II, LLC
C/O VENROCK
3340 HILLVIEW AVE.
PALO ALTO, CA 94304		     X    

Signatures

/s/ David L. Stepp, Authorized Signatory 06/17/2015
**Signature of Reporting Person Date
/s/ David L. Stepp, as attorney in fact 06/17/2015
**Signature of Reporting Person Date
/s/ David L. Stepp, as attorney in fact 06/17/2015
**Signature of Reporting Person Date

Explanation of Responses:

* If the form is filed by more than one reporting person, see Instruction 5(b)(v).
** Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
(1) Consists of: 2,736,388 shares held directly by Venrock Healthcare Capital Partners, L.P. ("VHCP"); 5,373,623 shares held directly by Venrock Healthcare Capital Partners II, L.P. ("VHCP II"); 500,409 shares held directly by VHCP Co-Investment Holdings, LLC ("Co-Invest"); and 2,178,904 shares held directly by VHCP Co-Investment Holdings II, LLC ("Co-Invest II").
(2) Consists of: 1,094,555 warrants held directly by VHCP; 2,149,449 warrants held directly by VHCP II; 200,164 warrants held directly by Co-Invest; and 871,562 warrants held directly by Co-Invest II.
(3) VHCP Management, LLC ("VHCP Management") is the general partner of VHCP and the manager of Co-Invest and may be deemed to beneficially own these shares. VHCP Management II, LLC ("VHCP Management II") is the general partner of VHCP II and the manager of Co-Invest II and may be deemed to beneficially own these shares. Drs. Anders D. Hove and Bong Y. Koh are the managing members of VHCP Management and VHCP Management II and may be deemed to beneficially own these shares. Drs. Hove and Koh, VHCP Management and VHCP Management II expressly disclaim beneficial ownership over these shares and warrants except to the extent of their indirect pecuniary interests therein.

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