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
OMB APPROVAL
OMB Number: 3235-0104
Expires: January 31, 2005
Estimated average burden hours per response... 0.5

(Print or Type Responses)
1. Name and Address of Reporting Person *
  Atlas Venture Fund VII L P
 2. Date of Event Requiring Statement (Month/Day/Year)
10/25/2012		 3. Issuer Name and Ticker or Trading Symbol
ARCA biopharma, Inc. [ABIO]
(Last)
(First)
(Middle)
25 FIRST STREET, SUITE 303		 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)

CAMBRIDGE, MA 02141		 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 1,579,542 (1)
D
 

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly. SEC 1473 (7-02)
Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB control number.

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
Warrant to Purchase Common Stock   (2) 10/10/2013 Common Stock 75,449 (1) $ 9.7406 D  
Warrant to Purchase Common Stock   (2) 10/25/2017 Common Stock 238,034 (1) $ 0.3001 D  

Reporting Owners

Reporting Owner Name / Address Relationships
Director 10% Owner Officer Other
Atlas Venture Fund VII L P
25 FIRST STREET, SUITE 303
CAMBRIDGE, MA 02141		     X    
Atlas Venture Associates VII, L.P.
25 FIRST STREET, SUITE 303
CAMBRIDGE, MA 02141		     X    

Signatures

Atlas Venture Fund VII, L.P. By: Atlas Venture Associates VII, L.P., its general partner By: Atlas Venture Associates VII, Inc., its general partner /s/ Kristen Laguerre Name: Kristen Laguerre Title: Vice President 11/02/2012
**Signature of Reporting Person Date
Atlas Venture Associates VII, L.P. By: Atlas Venture Associates VII, Inc., /s/ Kristen Laguerre Name: Kristen Laguerre Title: Vice President 11/02/2012
**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) Atlas Venture Fund VII, L.P. ("AV VII") is the record holder of these securities. Atlas Venture Associates VII, L.P. ("AVA VII LP") is the sole general partner of AV VII. Each of AV VII and AVA VII LP disclaims beneficial ownership of the reported securities except to the extent of their pecuniary interest therein.
(2) This warrant is immediately exercisable.

Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, See Instruction 6 for procedure.

Potential persons who are to respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB number.