ARCA BIOPHARMA, INC. 2004 STOCK INCENTIVE PLAN

This Option is only exercisable before it expires and then only with respect to the vested portion of the Option. Subject to the preceding sentence, you may exercise this Option, in whole or in part, to purchase a whole number of vested shares not less than one hundred (100) shares (unless the total number of vested shares under the Option is less than 100 shares, in which case you may purchase such total) by following the procedures set forth in the Plan and below in this Option Agreement.

Your right to purchase the Option Shares vests as follows: twenty-five percent (25%) vests one year after Vesting Start Date and 6.25% vests at the end of each three (3) month period thereafter. The resulting aggregate number of vested shares will be rounded to the nearest whole number, and you cannot vest in more than the number of Option Shares.

No additional Option Shares will vest after your Service has terminated for any reason. As described below, in certain cases this Option will expire after your Service, and the vesting of this Option has already terminated.

heirs may exercise the vested portion of this Option.

In addition, if you die during the ninety (90) day period described in connection with a regular termination (i.e., a termination of your Service not on account of your death, Disability or Cause), and a vested portion of this Option has not yet been exercised, then this Option will instead expire on the date twelve (12) months after your termination date. In such a case, during the period following your death up to the date twelve (12) months after your termination date, your estate or heirs may exercise the vested portion of this Option.

For purposes of this Option, your Service does not terminate when you go on a bona fide employee leave of absence that was approved by the Company in writing, if the terms of the leave provide for continued Service crediting, or when continued Service crediting is required by applicable law. However, your Service will be treated as terminating ninety (90) days after you went on employee leave, unless your right to return to active work is guaranteed by law or by a contract. Your Service terminates in any event when the approved leave ends unless you immediately return to active employee work.

The Company determines, in its sole discretion, which leaves count for this purpose, and when your Service terminates for all purposes under the Plan.

When you wish to exercise this Option, you must notify the Company by filing the proper “Notice of Exercise” form at the address given on the form. Your notice must specify how many shares you wish to purchase (in a parcel of at least one hundred (100) shares generally). Your notice must also specify how your shares of Stock should be registered (in your name only or in your and your spouse’s names as joint tenants with right of survivorship). The notice will be effective when it is received by the Company.

If someone else wants to exercise this Option after your death, that person must prove to the Company’s satisfaction that he or she is entitled to do so.

When you submit your notice of exercise, you must include payment of the option price for the shares you are purchasing. Payment may be made in one (or a combination) of the following forms:

•   Cash, your personal check, a cashier’s check, a money order or another cash equivalent acceptable to the Company.

•   Shares of Stock which have already been owned by you for more than six (6) months and that are owned free of any liens, claims, encumbrances or securities interests and which are surrendered to the Company; provided, that such tender would not violate the provisions of any law, regulation or agreement restricting the redemption of the Company’s stock. The value of the shares, as determined in good faith by the Company’s Board of Directors as of the effective date of the Option exercise, will be applied to the option

price.

•   To the extent a public market for the Stock exists as determined by the Company, by delivery (on a form prescribed by the Company) of an irrevocable direction to a licensed securities broker acceptable to the Company to sell Stock and to deliver all or part of the sale proceeds to the Company in payment of the aggregate option price and any withholding taxes.

During your lifetime, only you (or, in the event of your legal incapacity or incompetency, your guardian or legal representative) may exercise this Option. You cannot transfer or assign this Option. For instance, you may not sell this Option or use it as security for a loan. If you attempt to do any of these things, this Option will immediately become invalid. You may, however, dispose of this Option in your will or it may be transferred upon your death by the laws of descent and distribution.

Regardless of any marital property settlement agreement, the Company is not obligated to honor a notice of exercise from your spouse, nor is the Company obligated to recognize your spouse’s interest in this Option in any other way.

In the event that you propose to sell, pledge or otherwise transfer to a third party any Option Shares, or any interest in such Option Shares, the Company shall have the “Right of First Refusal” with respect to all (and not less than all) of such Option Shares. If you desire to transfer any Option Shares, you must give a written notice (a “Transfer Notice”) to the Company describing fully the proposed transfer, including the number of shares proposed to be transferred, the proposed transfer price and the name and address of the proposed transferee.

The Transfer Notice shall be signed both by you and by the proposed new transferee and must constitute a binding commitment of both parties to the transfer of the shares. The Company shall have the right to purchase all, and not less than all, of such Option Shares on the terms of the proposal described in the Transfer Notice (subject, however, to any change in such terms permitted in the next paragraph) by delivery of a notice of exercise of the Right of First Refusal within thirty (30) days after the date when the Transfer Notice was received by the Company.

If the Company fails to exercise its Right of First Refusal within thirty (30) days after the date when it received the Transfer Notice, you may, not later than ninety (90) days following receipt of the Transfer Notice by the Company, conclude a transfer of the Stock subject to the Transfer Notice on the terms and conditions described in the Transfer Notice. Any proposed transfer on terms and conditions different from those described in the Transfer Notice, as well as any subsequent proposed transfer by you, shall again be subject to the Right of First Refusal and shall require compliance with the procedure described in the paragraph above. If the Company exercises its Right of First Refusal, the parties shall consummate the sale of the Stock on the terms set forth in the Transfer Notice within sixty (60) days after the date when the Company received the Transfer Notice (or within such longer period as may have been specified in the Transfer Notice); provided, however, that in the event the Transfer Notice provided that payment for the Stock was to be made in a form other than lawful money paid at the time of transfer, the Company shall have the option of paying for the Stock with lawful money equal to the present value of the consideration described in the Transfer Notice.

In the case of any purchase of Stock under this Right of First Refusal, at the option of the Company, the Company may pay you the purchase price in three or fewer annual installments. Interest shall be credited on the installments at the applicable federal rate (as determined for purposes of Section 1274 of the Code) in effect on the date on which the purchase is made. The Company shall pay at least one-third of the total purchase price each year, plus interest on the unpaid balance, with the first payment being made on or before the sixtieth (60^th) day after the purchase.

The Company’s rights under this subsection shall be freely assignable, in whole or in part, shall inure to the benefit of its successors and assigns and shall be binding upon any transferee of the Option Shares.

The Company’s Right of First Refusal shall terminate in the event that the Stock is listed on an established national or regional stock exchange, is admitted for quotation on The Nasdaq Stock Market, Inc., or is publicly traded in an established securities market.

All certificates representing the Stock issued upon exercise of this Option shall, where applicable, have endorsed thereon the following legends:

“THE SHARES REPRESENTED BY THIS CERTIFICATE ARE SUBJECT TO CERTAIN RESTRICTIONS ON TRANSFER AND OPTIONS TO PURCHASE SUCH SHARES SET FORTH IN AN AGREEMENT BETWEEN THE COMPANY AND THE REGISTERED HOLDER, OR HIS OR HER PREDECESSOR IN INTEREST. A COPY OF SUCH AGREEMENT IS ON FILE AT THE PRINCIPAL OFFICE OF THE COMPANY AND WILL BE FURNISHED UPON WRITTEN REQUEST TO THE SECRETARY OF THE COMPANY BY THE HOLDER OF RECORD OF THE SHARES REPRESENTED BY THIS CERTIFICATE.”

The text of the Plan is incorporated in this Option Agreement by reference. Certain capitalized terms used in this Option Agreement are defined in the Plan, and have the meaning set forth in the Plan.

This Option Agreement and the Plan constitute the entire understanding between you and the Company regarding this Option. Any prior agreements, commitments or negotiations concerning this Option are superseded.