SEC Form 3

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 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person* Atlas Venture Fund VII L P (Last) (First) (Middle) 890 WINTER STREET, SUITE 320 (Street) WALTHAM MA 02451 (City) (State) (Zip)	2. Date of Event Requiring Statement (Month/Day/Year) 01/27/2009	3. Issuer Name and Ticker or Trading Symbol ARCA biopharma, Inc. [ ABIO ]
		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 of Original Filed (Month/Day/Year)
			6. Individual or Joint/Group Filing (Check Applicable Line) Form filed by One Reporting Person X Form filed by More than One Reporting Person

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	1,402,163(1)	D

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: 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(3)	$9.7406	D

1. Name and Address of Reporting Person* Atlas Venture Fund VII L P (Last) (First) (Middle) 890 WINTER STREET, SUITE 320 (Street) WALTHAM MA 02451 (City) (State) (Zip) Relationship of Reporting Person(s) to Issuer Director X 10% Owner Officer (give title below) Other (specify below)

1. Name and Address of Reporting Person* Atlas Venture Associates VII, L.P. (Last) (First) (Middle) 890 WINTER STREET, SUITE 320 (Street) WALTHAM MA 02451 (City) (State) (Zip) Relationship of Reporting Person(s) to Issuer Director X 10% Owner Officer (give title below) Other (specify below)

Explanation of Responses:

1. These shares are held directly by Atlas Venture Fund VII, L.P. Atlas Venture Associates VII, L.P. is the general partner of Atlas Venture Fund VII, L.P. Each of the Filing Persons disclaims beneficial ownership of the shares except to the extent of his or its pecuniary interest therein.

2. This warrant is immediately exercisable.

3. These warrants are held directly by Atlas Venture Fund VII, L.P. Atlas Venture Associates VII, L.P. is the general partner of Atlas Venture Fund VII, L.P. Each of the Filing Persons disclaims beneficial ownership of the warrants except to the extent of his or its pecuniary interest therein.

Remarks:

This statement on Form 3 is filed by Atlas Venture Fund VII, L.P. and Atlas Venture Associates VII, L.P. The principal business address for each of the reporting persons is 890 Winter Street, Suite 320, Waltham, Massachusetts 02451. The reporting persons disclaim beneficial ownership of the securities listed herein except to the extent of their pecuniary interest therein.

	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 By:/s/ Kristen Laguerre Name: Kristen Laguerre Title: Vice President	02/05/2009
	Atlas Venture Fund VII, L.P. By: Atlas Venture Associates VII, Inc. Its General Partner By: /s/ Kristen Laguerre Name: Kristen Laguerre Title: Vice President	02/05/2009
	** Signature of Reporting Person	Date
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 5 (b)(v).
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