Sec Form 4 Filing - VENROCK HEALTHCARE CAPITAL PARTNERS LP @ ARCA biopharma, Inc. - 2018-02-26

FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP 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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1. Name and Address of Reporting Person VENROCK HEALTHCARE CAPITAL PARTNERS LP 2. Issuer Name and Ticker or Trading Symbol ARCA biopharma, Inc. [ ABIO] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director X __ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) 3340 HILLVIEW AVENUE 3. Date of Earliest Transaction (MM/DD/YY) 02/26/2018 (Street) PALO ALTO, CA94304 4. If Amendment, Date Original Filed (MM/DD/YY) 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 Acquired, Disposed of, or Beneficially Owned 1.Title of Security (Instr. 3) 2. Transaction Date (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price Common Stock 02/26/2018 S 1,500,000 D $ 0.55 ( 1 ) 41,331 ( 2 ) I By Funds ( 3 ) Common Stock 02/27/2018 S 41,331 D $ 0.53 0 I By Funds ( 3 )

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned ( e.g. , puts, calls, warrants, options, convertible securities) 1. Title of Derivative Security (Instr. 3) 2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 4. Transaction Code (Instr. 8) 5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5) 6. Date Exercisable and Expiration Date (MM/DD/YY) 7. Title and Amount of Underlying Securities (Instr. 3 and 4) 8. Price of Derivative Security (Instr. 5) 9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4) 10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4) 11. Nature of Indirect Beneficial Ownership (Instr. 4) Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other VENROCK HEALTHCARE CAPITAL PARTNERS LP 3340 HILLVIEW AVENUE PALO ALTO, CA94304 X VHCP Co-Investment Holdings, LLC 3340 HILLVIEW AVENUE PALO ALTO, CA94304 X VHCP Management, LLC 3340 HILLVIEW AVENUE PALO ALTO, CA94304 X Venrock Healthcare Capital Partners II, L.P. 3340 HILLVIEW AVENUE PALO ALTO, CA94304 X VHCP Co-Investment Holdings II, LLC 3340 HILLVIEW AVENUE PALO ALTO, CA94304 X VHCP Management II, LLC 3340 HILLVIEW AVENUE PALO ALTO, CA94304 X Koh Bong Y 3340 HILLVIEW AVENUE PALO ALTO, CA94304 X Shah Nimish P 3340 HILLVIEW AVENUE PALO ALTO, CA94304 X Signatures /s/ David L. Stepp, Authorized Signatory 02/28/2018 Signature of Reporting Person Date /s/ David L. Stepp, as attorney in fact 02/28/2018 Signature of Reporting Person Date

Explanation of Responses:

( 1 )The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $0.50 to $0.63, inclusive. The reporting persons undertake to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the ranges set forth in this footnote (1) to this Form 4. ( 2 )Consists of: 10,482 shares held directly by Venrock Healthcare Capital Partners, L.P. ("VHCP"); 20,585 shares held directly by Venrock Healthcare Capital Partners II, L.P. ("VHCP II"); 1,917 shares held directly by VHCP Co-Investment Holdings, LLC ("Co-Invest"); and 8,347 shares held directly by VHCP Co-Investment Holdings II, LLC ("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. Bong Koh and Nimish Shah are the managing members of VHCP Management and VHCP Management II and may be deemed to beneficially own these shares. Drs. Koh and Shah, VHCP Management and VHCP Management II expressly disclaim beneficial ownership over these shares except to the extent of their indirect pecuniary interests therein.

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.

* If the form is filed by more than one reporting person, see Instruction 4(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).

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