SCHEDULE 13G/A

Under the Securities Exchange Act of 1934
(Amendment No. 2)*

(Name of Issuer)

(Title of Class of Securities)

(CUSIP Number)

(Date of Event Which Requires Filing of this Statement)

Check the appropriate box to designate the rule pursuant to which this Schedule is filed:

*The remainder of this cover page shall be filled out for a reporting person's initial filing on this form with respect to the subject class of securities, and for any subsequent amendment containing information which would alter disclosures provided in a prior cover page.

The information required on the remainder of this cover page shall not be deemed to be "filed" for the purpose of Section 18 of the Securities Exchange Act of 1934 ("Act") or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

(1)                                 Venrock Healthcare Capital Partners, L.P. (“VHCP”); Venrock Healthcare Capital Partners II, L.P. (“VHCP II”); VCHP Co-Investment Holdings, LLC (“Co-Invest”); VHCP Co-Investment Holdings II, LLC (“Co-Invest II”); VCHP Management, LLC; VCHP Management II, LLC; Nimish Shah and Bong Koh are members of a group for the purposes of this Schedule 13G/A.

(2)                                 Consists of: (i) 390,912 shares of common stock held directly by VHCP and 156,365 shares of common stock currently exercisable under a warrant held by VHCP; (ii) 767,660 shares of common stock held directly by VHCP II and 307,064 shares of common stock currently exercisable under a warrant held by VHCP II; (iii) 71,487 shares of common stock held directly by Co-Invest and 28,595 shares of common stock currently exercisable under a warrant held by Co-Invest; and (iv) 311,272 shares of common stock held directly by Co-Invest II and 124,509 shares of common stock currently exercisable under a warrant held by Co-Invest II.

(3)                                 This percentage is calculated based upon (i) 11,750,977 shares of the Issuer’s common stock outstanding as of November 7, 2017, as set forth in the Issuer’s Quarterly Report on Form 10-Q filed with the Securities and Exchange Commission on November 9, 2017, plus (ii) 616,533 shares of common stock underlying currently exercisable warrants held by the Reporting Persons.

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(1)                                 Venrock Healthcare Capital Partners, L.P. (“VHCP”); Venrock Healthcare Capital Partners II, L.P. (“VHCP II”); VCHP Co-Investment Holdings, LLC (“Co-Invest”); VHCP Co-Investment Holdings II, LLC (“Co-Invest II”); VCHP Management, LLC; VCHP Management II, LLC; Nimish Shah and Bong Koh are members of a group for the purposes of this Schedule 13G/A.

(2)                                 Consists of: (i) 390,912 shares of common stock held directly by VHCP and 156,365 shares of common stock currently exercisable under a warrant held by VHCP; (ii) 767,660 shares of common stock held directly by VHCP II and 307,064 shares of common stock currently exercisable under a warrant held by VHCP II; (iii) 71,487 shares of common stock held directly by Co-Invest and 28,595 shares of common stock currently exercisable under a warrant held by Co-Invest; and (iv) 311,272 shares of common stock held directly by Co-Invest II and 124,509 shares of common stock currently exercisable under a warrant held by Co-Invest II.

(3)                                 This percentage is calculated based upon (i) 11,750,977 shares of the Issuer’s common stock outstanding as of November 7, 2017, as set forth in the Issuer’s Quarterly Report on Form 10-Q filed with the Securities and Exchange Commission on November 9, 2017, plus (ii) 616,533 shares of common stock underlying currently exercisable warrants held by the Reporting Persons.

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(1)                                 Venrock Healthcare Capital Partners, L.P. (“VHCP”); Venrock Healthcare Capital Partners II, L.P. (“VHCP II”); VCHP Co-Investment Holdings, LLC (“Co-Invest”); VHCP Co-Investment Holdings II, LLC (“Co-Invest II”); VCHP Management, LLC; VCHP Management II, LLC; Nimish Shah and Bong Koh are members of a group for the purposes of this Schedule 13G/A.

(2)                                 Consists of: (i) 390,912 shares of common stock held directly by VHCP and 156,365 shares of common stock currently exercisable under a warrant held by VHCP; (ii) 767,660 shares of common stock held directly by VHCP II and 307,064 shares of common stock currently exercisable under a warrant held by VHCP II; (iii) 71,487 shares of common stock held directly by Co-Invest and 28,595 shares of common stock currently exercisable under a warrant held by Co-Invest; and (iv) 311,272 shares of common stock held directly by Co-Invest II and 124,509 shares of common stock currently exercisable under a warrant held by Co-Invest II.

(3)                                 This percentage is calculated based upon (i) 11,750,977 shares of the Issuer’s common stock outstanding as of November 7, 2017, as set forth in the Issuer’s Quarterly Report on Form 10-Q filed with the Securities and Exchange Commission on November 9, 2017, plus (ii) 616,533 shares of common stock underlying currently exercisable warrants held by the Reporting Persons.

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(1)                                 Venrock Healthcare Capital Partners, L.P. (“VHCP”); Venrock Healthcare Capital Partners II, L.P. (“VHCP II”); VCHP Co-Investment Holdings, LLC (“Co-Invest”); VHCP Co-Investment Holdings II, LLC (“Co-Invest II”); VCHP Management, LLC; VCHP Management II, LLC; Nimish Shah and Bong Koh are members of a group for the purposes of this Schedule 13G/A.

(2)                                 Consists of: (i) 390,912 shares of common stock held directly by VHCP and 156,365 shares of common stock currently exercisable under a warrant held by VHCP; (ii) 767,660 shares of common stock held directly by VHCP II and 307,064 shares of common stock currently exercisable under a warrant held by VHCP II; (iii) 71,487 shares of common stock held directly by Co-Invest and 28,595 shares of common stock currently exercisable under a warrant held by Co-Invest; and (iv) 311,272 shares of common stock held directly by Co-Invest II and 124,509 shares of common stock currently exercisable under a warrant held by Co-Invest II.

(3)                                 This percentage is calculated based upon (i) 11,750,977 shares of the Issuer’s common stock outstanding as of November 7, 2017, as set forth in the Issuer’s Quarterly Report on Form 10-Q filed with the Securities and Exchange Commission on November 9, 2017, plus (ii) 616,533 shares of common stock underlying currently exercisable warrants held by the Reporting Persons.

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(1)                                 Venrock Healthcare Capital Partners, L.P. (“VHCP”); Venrock Healthcare Capital Partners II, L.P. (“VHCP II”); VCHP Co-Investment Holdings, LLC (“Co-Invest”); VHCP Co-Investment Holdings II, LLC (“Co-Invest II”); VCHP Management, LLC; VCHP Management II, LLC; Nimish Shah and Bong Koh are members of a group for the purposes of this Schedule 13G/A.

(2)                                 Consists of: (i) 390,912 shares of common stock held directly by VHCP and 156,365 shares of common stock currently exercisable under a warrant held by VHCP; (ii) 767,660 shares of common stock held directly by VHCP II and 307,064 shares of common stock currently exercisable under a warrant held by VHCP II; (iii) 71,487 shares of common stock held directly by Co-Invest and 28,595 shares of common stock currently exercisable under a warrant held by Co-Invest; and (iv) 311,272 shares of common stock held directly by Co-Invest II and 124,509 shares of common stock currently exercisable under a warrant held by Co-Invest II.

(3)                                 This percentage is calculated based upon (i) 11,750,977 shares of the Issuer’s common stock outstanding as of November 7, 2017, as set forth in the Issuer’s Quarterly Report on Form 10-Q filed with the Securities and Exchange Commission on November 9, 2017, plus (ii) 616,533 shares of common stock underlying currently exercisable warrants held by the Reporting Persons.

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(1)                                 Venrock Healthcare Capital Partners, L.P. (“VHCP”); Venrock Healthcare Capital Partners II, L.P. (“VHCP II”); VCHP Co-Investment Holdings, LLC (“Co-Invest”); VHCP Co-Investment Holdings II, LLC (“Co-Invest II”); VCHP Management, LLC; VCHP Management II, LLC; Nimish Shah and Bong Koh are members of a group for the purposes of this Schedule 13G/A.

(2)                                 Consists of: (i) 390,912 shares of common stock held directly by VHCP and 156,365 shares of common stock currently exercisable under a warrant held by VHCP; (ii) 767,660 shares of common stock held directly by VHCP II and 307,064 shares of common stock currently exercisable under a warrant held by VHCP II; (iii) 71,487 shares of common stock held directly by Co-Invest and 28,595 shares of common stock currently exercisable under a warrant held by Co-Invest; and (iv) 311,272 shares of common stock held directly by Co-Invest II and 124,509 shares of common stock currently exercisable under a warrant held by Co-Invest II.

(3)                                 This percentage is calculated based upon (i) 11,750,977 shares of the Issuer’s common stock outstanding as of November 7, 2017, as set forth in the Issuer’s Quarterly Report on Form 10-Q filed with the Securities and Exchange Commission on November 9, 2017, plus (ii) 616,533 shares of common stock underlying currently exercisable warrants held by the Reporting Persons.

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(1)                                 Venrock Healthcare Capital Partners, L.P. (“VHCP”); Venrock Healthcare Capital Partners II, L.P. (“VHCP II”); VCHP Co-Investment Holdings, LLC (“Co-Invest”); VHCP Co-Investment Holdings II, LLC (“Co-Invest II”); VCHP Management, LLC; VCHP Management II, LLC; Nimish Shah and Bong Koh are members of a group for the purposes of this Schedule 13G/A.

(2)                                 Consists of: (i) 390,912 shares of common stock held directly by VHCP and 156,365 shares of common stock currently exercisable under a warrant held by VHCP; (ii) 767,660 shares of common stock held directly by VHCP II and 307,064 shares of common stock currently exercisable under a warrant held by VHCP II; (iii) 71,487 shares of common stock held directly by Co-Invest and 28,595 shares of common stock currently exercisable under a warrant held by Co-Invest; and (iv) 311,272 shares of common stock held directly by Co-Invest II and 124,509 shares of common stock currently exercisable under a warrant held by Co-Invest II.

(3)                                 This percentage is calculated based upon (i) 11,750,977 shares of the Issuer’s common stock outstanding as of November 7, 2017, as set forth in the Issuer’s Quarterly Report on Form 10-Q filed with the Securities and Exchange Commission on November 9, 2017, plus (ii) 616,533 shares of common stock underlying currently exercisable warrants held by the Reporting Persons.

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(1)                                 Venrock Healthcare Capital Partners, L.P. (“VHCP”); Venrock Healthcare Capital Partners II, L.P. (“VHCP II”); VCHP Co-Investment Holdings, LLC (“Co-Invest”); VHCP Co-Investment Holdings II, LLC (“Co-Invest II”); VCHP Management, LLC; VCHP Management II, LLC; Nimish Shah and Bong Koh are members of a group for the purposes of this Schedule 13G/A.

(2)                                 Consists of: (i) 390,912 shares of common stock held directly by VHCP and 156,365 shares of common stock currently exercisable under a warrant held by VHCP; (ii) 767,660 shares of common stock held directly by VHCP II and 307,064 shares of common stock currently exercisable under a warrant held by VHCP II; (iii) 71,487 shares of common stock held directly by Co-Invest and 28,595 shares of common stock currently exercisable under a warrant held by Co-Invest; and (iv) 311,272 shares of common stock held directly by Co-Invest II and 124,509 shares of common stock currently exercisable under a warrant held by Co-Invest II.

(3)                                 This percentage is calculated based upon (i) 11,750,977 shares of the Issuer’s common stock outstanding as of November 7, 2017, as set forth in the Issuer’s Quarterly Report on Form 10-Q filed with the Securities and Exchange Commission on November 9, 2017, plus (ii) 616,533 shares of common stock underlying currently exercisable warrants held by the Reporting Persons.

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Introductory Note: This Schedule 13G/A is filed on behalf of Venrock Healthcare Capital Partners, L.P., a limited partnership organized under the laws of the state of Delaware (“VHCP”), Venrock Healthcare Capital Partners II, L.P., a limited partnership organized under the laws of the state of Delaware (“VHCP II”), VHCP Co-Investment Holdings, LLC., a limited liability company organized under the laws of the state of Delaware (“Co-Invest”), VHCP Co-Investment Holdings II, LLC, a limited liability company organized under the laws of the state of Delaware (“Co-Invest II), VCHP Management, LLC, a limited liability company organized under the laws of the state of Delaware, VCHP Management II, LLC, a limited liability company organized under the laws of the state of Delaware, Nimish Shah and Bong Koh in respect of the shares of common stock of ARCA biopharma, Inc.

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(1)   These shares are owned directly as follows: (i) 390,912 shares of common stock are held directly by VHCP and 156,365 shares of common stock are currently exercisable under a warrant held by VHCP; (ii) 767,660 shares of common stock are held directly by VHCP II and 307,064 shares of common stock are currently exercisable under a warrant held by VHCP II; (iii) 71,487 shares of common stock are held directly by Co-Invest and 28,595 shares of common stock are currently exercisable under a warrant held by Co-Invest; and (iv) 311,272 shares of common stock are held directly by Co-Invest II and 124,509 shares of common stock are currently exercisable under a warrant held by Co-Invest II.

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SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

Date: February 13, 2018

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EXHIBITS

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EXHIBIT A

JOINT FILING AGREEMENT

In accordance with Rule 13d-1(k) under the Securities Exchange Act of 1934, as amended, the undersigned agree to the joint filing on behalf of each of them of a statement on Schedule 13G (including amendments thereto) with respect to the Common Stock of ARCA biopharma, Inc. and further agree that this agreement be included as an exhibit to such filing. Each party to the agreement expressly authorizes each other party to file on its behalf any and all amendments to such statement. Each party to this agreement agrees that this joint filing agreement may be signed in counterparts.

In evidence whereof, the undersigned have caused this Agreement to be executed on their behalf this 13th day of February, 2018.

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EXHIBIT B

POWER OF ATTORNEY FOR NIMISH SHAH

KNOW ALL BY THESE PRESENTS, that the undersigned hereby constitutes and appoints each of David L. Stepp, Sherman G. Souther and Lisa D. Harris signing individually, the undersigned’s true and lawful attorney-in fact and agent to:

The undersigned hereby grants to such attorney-in-fact full power and authority to do and perform any and every act and thing whatsoever requisite, necessary, or proper to be done in the exercise of any of the rights and powers herein granted, as fully to all intents and purposes as the undersigned might or could do if personally present, with full power of substitution or revocation, hereby ratifying and confirming all that such attorney-in-fact, or such attorney-in-fact’s substitute or substitutes, shall lawfully do or cause to be done by virtue of this power of attorney and the rights and powers herein granted. The undersigned acknowledges that the foregoing attorney-in-fact, in serving in such capacity at the request of undersigned, is not assuming, nor is Venrock assuming, any of the undersigned’s responsibilities to comply with the Exchange Act, including without limitation Sections 13 and 16 of the Exchange Act.

This power of Attorney shall remain in full force and effect until the earliest to occur of (a) the undersigned is no longer required to file any form or document with respect to the undersigned’s holdings of and transactions in securities issued by a company, (b) revocation by the undersigned in a signed writing delivered to the foregoing attorney-in-fact, or (c) until such attorney-in-fact shall no longer be employed by VR Management, LLC (or its successor).

IN WITNESS WHEREOF, the undersigned has cause this Power of Attorney to be executed as of this 13th  day of February, 2017.

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