Document:

Form of Registration Rights Agreement

 Exhibit 10.2 
 REGISTRATION RIGHTS AGREEMENT 
 This REGISTRATION RIGHTS AGREEMENT
(this “Agreement”), dated as of December     , 2012, is by and among ARCA biopharma, Inc., a Delaware corporation (the “Company”), and the undersigned buyer ( “Buyer”).

 RECITALS 
 A. In connection with that certain Subscription Agreement by and between the Company and Buyer, dated as of December     , 2012 (the “Securities Purchase Agreement”),
the Company has agreed, upon the terms and subject to the conditions of the Securities Purchase Agreement, to issue and sell to Buyer (i) shares (the “Common Shares”) of Common Stock (as defined in the Securities Purchase
Agreement) and (ii) the Warrants (as defined in the Securities Purchase Agreement), which will be exercisable for Warrant Shares (as defined in the Securities Purchase Agreement) in accordance with the terms of the Warrants. 

B. To induce the Buyer to consummate the transactions contemplated by the Securities Purchase Agreement, the Company has agreed to
provide certain registration rights under the Securities Act of 1933, as amended, and the rules and regulations thereunder, or any similar successor statute (collectively, the “1933 Act”), and applicable state securities laws.

 AGREEMENT 
 NOW, THEREFORE, in consideration of the premises and the mutual covenants contained herein and for other good and valuable consideration, the receipt and sufficiency of which are hereby
acknowledged, the Company and the Buyer hereby agree as follows: 
  

	1.	Definitions. 

 Capitalized
terms used herein and not otherwise defined herein shall have the respective meanings set forth in the Securities Purchase Agreements. As used in this Agreement, the following terms shall have the following meanings: 

(a) “Business Day” means any day other than Saturday, Sunday or any other day on which commercial banks in New York, New
York are authorized or required by law or other governmental action to remain closed. 
 (b) “Closing Date”
shall have the meaning set forth in the Securities Purchase Agreements. 
 (c) “Effective Date” means the date
that the applicable Registration Statement has been declared effective by the SEC. 
 (d)
“Effectiveness Deadline” means (i) with respect to the initial Registration Statement required to be filed pursuant to Section 2(a), the earlier of the (A) 90th calendar day after the Closing Date (or the 120th calendar day after the Closing Date in the event that such Registration Statement is subject to review by the SEC) and
(B) 4th Business Day after the date the Company is
notified (orally or in writing, whichever is earlier) by the SEC that such 

 
Registration Statement will not be reviewed or will not be subject to further review and (ii) with respect to any additional Registration Statements that may be required to be filed by the
Company pursuant to this Agreement, the earlier of the (A) 75th calendar day following the date on which the Company was required to file such additional Registration Statement (or the 105th calendar day after such date in the event that such Registration Statement is subject to review by the SEC) and
(B) 4th Business Day after the date the Company is
notified (orally or in writing, whichever is earlier) by the SEC that such Registration Statement will not be reviewed or will not be subject to further review. 

(e) “Filing Deadline” means (i) with respect to the initial Registration Statement required to
be filed pursuant to Section 2(a), the 60th calendar
day after the Closing Date and (ii) with respect to any additional Registration Statements that may be required to be filed by the Company pursuant to this Agreement, the date on which the Company was required to file such additional
Registration Statement pursuant to the terms of this Agreement. 
 (f) “Investor” means Buyer or any transferee
or assignee of any Registrable Securities or Warrants, as applicable, to whom Buyer assigns its rights under this Agreement and who agrees to become bound by the provisions of this Agreement in accordance with Section 9 and any transferee or
assignee thereof to whom a transferee or assignee of any Registrable Securities or Warrants, as applicable, assigns its rights under this Agreement and who agrees to become bound by the provisions of this Agreement in accordance with Section 9.

 (g) “Person” means an individual, a limited liability company, a partnership, a joint venture, a
corporation, a trust, an unincorporated organization or a government or any department or agency thereof. 
 (h)
“register,” “registered,” and “registration” refer to a registration effected by preparing and filing one or more Registration Statements in compliance with the 1933 Act and pursuant to Rule 415 and
the declaration of effectiveness of such Registration Statement(s) by the SEC. 
 (i) “Registrable Securities”
means (i) the Common Shares, (ii) the Warrant Shares and (iii) any capital stock of the Company issued or issuable with respect to the Common Shares, the Warrant Shares or the Warrants, including, without limitation, (1) as a
result of any stock split, stock dividend, recapitalization, exchange or similar event or otherwise and (2) shares of capital stock of the Company into which the shares of Common Stock are converted or exchanged and shares of capital stock of a
Successor Entity (as defined in the Warrants) into which the shares of Common Stock are converted or exchanged, in each case, without regard to any limitations on exercise of the Warrants. 

(j) “Registration Statement” means a registration statement or registration statements of the Company filed under the
1933 Act covering Registrable Securities. 
 (k) “Required Investors” means the holders of at least 66 2/3% of
the Registrable Securities. 
 (l) “Required Registration Amount” means the sum of (i) the Common Shares
issued and (ii) the maximum number of Warrant Shares issued and issuable pursuant to the 

  
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Warrants as of the Trading Day (as defined in the Warrants) immediately preceding the applicable date of determination (without taking into account any limitations on the exercise of the Warrants
set forth therein), all subject to adjustment as provided in Section 2(c). 
 (m) “Rule 144” means Rule
144 promulgated by the SEC under the 1933 Act, as such rule may be amended from time to time, or any other similar or successor rule or regulation of the SEC that may at any time permit the Investors to sell securities of the Company to the public
without registration. 
 (n) “Rule 415” means Rule 415 promulgated by the SEC under the 1933 Act, as such rule
may be amended from time to time, or any other similar or successor rule or regulation of the SEC providing for offering securities on a continuous or delayed basis. 
 (o) “SEC” means the United States Securities and Exchange Commission or any successor thereto. 
  

	2.	Registration. 

 (a)
Mandatory Registration. The Company shall prepare and, as soon as practicable, but in no event later than the Filing Deadline, file with the SEC an initial Registration Statement on Form S-3 covering the resale of all of the Registrable
Securities provided that such initial Registration Statement shall register for resale at least the number of shares of Common Stock equal to the Required Registration Amount as of the date such Registration Statement is initially filed with the
SEC, provided further that if Form S-3 is unavailable for such a registration, the Company shall use such other form as is required by Section 2(b). Such initial Registration Statement, and each other Registration Statement required to be filed
pursuant to the terms of this Agreement, shall contain (except if otherwise directed by the Required Investors) the “Selling Stockholders” and “Plan of Distribution” sections in substantially the form attached
hereto as Exhibit B, unless otherwise required by Staff (as defined below) comments. The Company shall use commercially reasonable efforts to have such initial Registration Statement, and each other Registration Statement required to
be filed pursuant to the terms of this Agreement, declared effective by the SEC as soon as practicable, but in no event later than the applicable Effectiveness Deadline for such Registration Statement. 

(b) Ineligibility to Use Form S-3. In the event that Form S-3 is not available for the registration of the resale of Registrable
Securities hereunder, the Company shall use commercially reasonable efforts to (i) register the resale of the Registrable Securities on another appropriate form and (ii) undertake to register the resale of the Registrable Securities on
Form S-3 as soon as such form is available, provided that the Company shall maintain the effectiveness of all Registration Statements then in effect and the availability for use of each prospectus contained therein until such time as a Registration
Statement on Form S-3 covering the resale of all the Registrable Securities has been declared effective by the SEC and the prospectus contained therein is available for use. 
 (c) Sufficient Number of Shares Registered. In the event the number of shares available under any Registration Statement is insufficient to cover all of the Registrable Securities required to be
covered by such Registration Statement or an Investor’s allocated 

  
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portion of the Registrable Securities pursuant to Section 2(e), the Company shall amend such Registration Statement (if permissible), or file with the SEC a new Registration Statement (on
the short form available therefor, if applicable), or both, so as to cover at least the Required Registration Amount as of the Trading Day immediately preceding the date of the filing of such amendment or new Registration Statement, in each case, as
soon as practicable, but in any event not later than fifteen (15) days after the necessity therefor arises (but taking account of any Staff position with respect to the date on which the Staff will permit such amendment to the Registration
Statement and/or such new Registration Statement (as the case may be) to be filed with the SEC). The Company shall use its commercially reasonable efforts to cause such amendment to such Registration Statement and/or such new Registration Statement
(as the case may be) to become effective as soon as practicable following the filing thereof with the SEC, but in no event later than the applicable Effectiveness Deadline for such Registration Statement. For purposes of the foregoing provision, the
number of shares available under a Registration Statement shall be deemed “insufficient to cover all of the Registrable Securities” if at any time the number of shares of Common Stock available for resale under the applicable Registration
Statement is less than the product determined by multiplying (i) the Required Registration Amount as of such time by (ii) 0.90. The calculation set forth in the foregoing sentence shall be made without regard to any limitations on exercise
of the Warrants (and such calculation shall assume that the Warrants are then fully exercisable for shares of Common Stock at the then-prevailing applicable Exercise Price). 
 (d) Offering. Notwithstanding anything to the contrary contained in this Agreement, in the event the staff of the SEC (the “Staff”) or the SEC seeks to characterize
any offering pursuant to a Registration Statement filed pursuant to this Agreement as constituting an offering of securities by, or on behalf of, the Company, or in any other manner, such that the Staff or the SEC do
not permit such Registration Statement to become effective and used for resales in a manner that does not constitute such an offering and that permits the continuous resale at the market by the Investors participating therein (or as
otherwise may be acceptable to each Investor) without being named therein as an “underwriter,” then the Company shall reduce the number of shares to be included in such Registration Statement by all Investors until such time as the
Staff and the SEC shall so permit such Registration Statement to become effective as aforesaid. In making such reduction, the Company shall reduce the number of shares to be included by all Investors on a pro rata basis (based upon the
number of Registrable Securities otherwise required to be included for each Investor) unless the inclusion of shares by a particular Investor or a particular set of Investors are resulting in the Staff or the SEC’s “by or on behalf of
the Company” offering position, in which event the shares held by such Investor or set of Investors shall be the only shares subject to reduction (and if by a set of Investors on a pro rata basis by such Investors or on such other basis as
would result in the exclusion of the least number of shares by all such Investors). In addition, in the event that the Staff or the SEC requires any Investor seeking to sell securities under a Registration Statement filed pursuant to this
Agreement to be specifically identified as an “underwriter” in order to permit such Registration Statement to become effective, and such Investor does not consent to being so named as an underwriter in such Registration
Statement, then, in each such case, the Company shall reduce the total number of Registrable Securities to be registered on behalf of such Investor, until such time as the Staff or the SEC does not require such
identification or until such Investor accepts such identification and the manner thereof. Any reduction pursuant to this paragraph will first reduce all securities that are not Registrable Securities, if any such

  
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securities are permitted by the Required Holders to be included in accordance with the terms of this Agreement. In the event of any reduction in Registrable Securities pursuant to this
paragraph, an affected Investor shall have the right to require, upon delivery of a written request to the Company signed by such Investor, the Company to file a registration statement within thirty (30) days of such request (subject to any
restrictions imposed by Rule 415 or required by the Staff or the SEC) for resale by such Investor in a manner acceptable to such Investor, and the Company shall following such request cause to be and keep effective such registration
statement in the same manner as otherwise contemplated in this Agreement for registration statements hereunder, in each case until such time as: (i) all Registrable Securities held by such Investor have been registered and sold
pursuant to an effective Registration Statement in a manner acceptable to such Investor or (ii) all Registrable Securities may be resold by such Investor without restriction (including, without limitation, volume limitations) pursuant
to Rule 144 (taking account of any Staff position with respect to “affiliate” status) and without the need for current public information required by Rule 144(c)(1) (or Rule 144(i)(2), if applicable) or (iii) such Investor agrees to
be named as an underwriter in any such Registration Statement in a manner acceptable to such Investor as to all Registrable Securities held by such Investor and that have not theretofore been included in a Registration Statement under this Agreement
(it being understood that the special demand right under this sentence may be exercised by an Investor multiple times and with respect to limited amounts of Registrable Securities in order to permit the resale thereof by such Investor as
contemplated above). 
 (e) Allocation of Registrable Securities. The initial number of Registrable Securities included
in any Registration Statement and any increase in the number of Registrable Securities included therein shall be allocated pro rata among the Investors based on the number of Registrable Securities held by each Investor at the time such Registration
Statement covering such initial number of Registrable Securities or increase thereof is declared effective by the SEC. In the event that an Investor sells or otherwise transfers any of such Investor’s Registrable Securities, each transferee or
assignee (as the case may be) that becomes an Investor shall be allocated a pro rata portion of the then-remaining number of Registrable Securities included in such Registration Statement for such transferor or assignee (as the case may be). Any
shares of Common Stock included in a Registration Statement and which remain allocated to any Person which ceases to hold any Registrable Securities covered by such Registration Statement shall be allocated to the remaining Investors, pro rata based
on the number of Registrable Securities then held by such Investors which are covered by such Registration Statement. 
  

	3.	Related Obligations. 

 The
Company shall use commercially reasonable efforts to effect the registration of the Registrable Securities in accordance with the intended method of disposition thereof, and, pursuant thereto, the Company shall have the following obligations:

 (a) The Company shall promptly prepare and file with the SEC a Registration Statement with respect to all the Registrable
Securities (but in no event later than the applicable Filing Deadline) and use commercially reasonable efforts to cause such Registration Statement to become effective as soon as practicable after such filing (but in no event later than the
Effectiveness Deadline). Subject to Allowable Grace Periods, the Company shall keep each Registration Statement effective (and the prospectus contained therein available for use) pursuant 

  
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to Rule 415 for resales by the Investors on a delayed or continuous basis at then-prevailing market prices (and not fixed prices) at all times until the earlier of (i) the date as of which
all of the Investors may sell all of the Registrable Securities required to be covered by such Registration Statement (disregarding any reduction pursuant to Section 2(d)) without restriction pursuant to Rule 144 (including, without limitation,
volume restrictions) and without the need for current public information required by Rule 144(c)(1) (or Rule 144(i)(2), if applicable) or (ii) the date on which the Investors shall have sold all of the Registrable Securities covered by such
Registration Statement (the “Registration Period”). Notwithstanding anything to the contrary contained in this Agreement, the Company shall ensure that, when filed and at all times while effective, each Registration Statement
(including, without limitation, all amendments and supplements thereto) and the prospectus (including, without limitation, all amendments and supplements thereto) used in connection with such Registration Statement (1) shall not contain any
untrue statement of a material fact or omit to state a material fact required to be stated therein, or necessary to make the statements therein (in the case of prospectuses, in the light of the circumstances in which they were made) not misleading
and (2) will disclose (whether directly or through incorporation by reference to other SEC filings to the extent permitted) all material information regarding the Company and its securities. The Company shall submit to the SEC, within five
(5) Business Days after the Company learns that no review of a particular Registration Statement will be made by the Staff or that the Staff has no further comments on a particular Registration Statement (as the case may be) a request for
acceleration of effectiveness of such Registration Statement to a time and date not later than forty-eight (48) hours after the submission of such request. 
 (b) The Company shall prepare and file with the SEC such amendments (including, without limitation, post-effective amendments) and supplements to each Registration Statement and the prospectus used in
connection with each such Registration Statement, which prospectus is to be filed pursuant to Rule 424 promulgated under the 1933 Act, as may be necessary to keep each such Registration Statement effective at all times during the Registration Period
for such Registration Statement, and, during such period, comply with the provisions of the 1933 Act with respect to the disposition of all Registrable Securities of the Company required to be covered by such Registration Statement until such time
as all of such Registrable Securities shall have been disposed of in accordance with the intended methods of disposition by the seller or sellers thereof as set forth in such Registration Statement. In the case of amendments and supplements to any
Registration Statement which are required to be filed pursuant to this Agreement (including, without limitation, pursuant to this Section 3(b)) by reason of the Company filing a report on Form 10-Q or Form 10-K or any analogous report under the
Securities Exchange Act of 1934, as amended (the “1934 Act”), the Company shall have incorporated such report by reference into such Registration Statement, if applicable, or shall file such amendments or supplements with the SEC on
the same day on which the 1934 Act report is filed which created the requirement for the Company to amend or supplement such Registration Statement. 
 (c) The Company shall promptly furnish to each Investor whose Registrable Securities are included in any Registration Statement, without charge, (i) after the same is prepared and filed with the SEC,
at least one (1) copy of each Registration Statement and any amendment(s) and supplement(s) thereto, including, without limitation, financial statements and schedules, all documents incorporated therein by reference, if requested by an
Investor, all 

  
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exhibits and each preliminary prospectus, (ii) upon the effectiveness of each Registration Statement, ten (10) copies of the prospectus included in such Registration Statement and all
amendments and supplements thereto (or such other number of copies as such Investor may reasonably request from time to time) and (iii) such other documents, including, without limitation, copies of any preliminary or final prospectus, as such
Investor may reasonably request from time to time in order to facilitate the disposition of the Registrable Securities owned by such Investor. 
 (d) The Company shall notify each Investor in writing of the happening of any event, as promptly as practicable after becoming aware of such event, as a result of which the prospectus included in a
Registration Statement, as then in effect, includes an untrue statement of a material fact or omission to state a material fact required to be stated therein or necessary to make the statements therein, in the light of the circumstances under which
they were made, not misleading (provided that in no event shall such notice contain any material, non-public information regarding the Company or any of its Subsidiaries), and, subject to Section 3(p), promptly prepare a supplement or amendment
to such Registration Statement and such prospectus contained therein to correct such untrue statement or omission and deliver ten (10) copies of such supplement or amendment to each Investor (or such other number of copies as such Investor may
reasonably request). The Company shall also promptly notify each Investor in writing (i) when a prospectus or any prospectus supplement or post-effective amendment has been filed, when a Registration Statement or any post-effective amendment
has become effective (notification of such effectiveness shall be delivered to each Investor by facsimile or e-mail on the same day of such effectiveness and by overnight mail), and when the Company receives written notice from the SEC that a
Registration Statement or any post-effective amendment will be reviewed by the SEC, (ii) of any request by the SEC for amendments or supplements to a Registration Statement or related prospectus or related information, (iii) of the
Company’s reasonable determination that a post-effective amendment to a Registration Statement would be appropriate; and (iv) of the receipt of any request by the SEC or any other federal or state governmental authority for any additional
information relating to the Registration Statement or any amendment or supplement thereto or any related prospectus. The Company shall respond as promptly as practicable to any comments received from the SEC with respect to each Registration
Statement or any amendment thereto (it being understood and agreed that the Company’s response to any such comments shall be delivered to the SEC no later than ten (10) Business Days after the receipt thereof). 

(e) The Company shall (i) use commercially reasonable efforts to prevent the issuance of any stop order or other suspension of
effectiveness of each Registration Statement or the use of any prospectus contained therein, or the suspension of the qualification, or the loss of an exemption from qualification, of any of the Registrable Securities for sale in any jurisdiction
and, if such an order or suspension is issued, to obtain the withdrawal of such order or suspension at the earliest possible moment and (ii) notify each Investor who holds Registrable Securities of the issuance of such order and the resolution
thereof or its receipt of actual notice of the initiation or threat of any proceeding for such purpose. 
 (f) If any Investor
may be required under applicable securities law to be described in any Registration Statement as an underwriter and such Investor consents to so being named an underwriter, at the request of any Investor, the Company shall furnish to such Investor,
on the 

  
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date of the effectiveness of such Registration Statement and thereafter from time to time on such dates as an Investor may reasonably request (i) a letter, dated such date, from the
Company’s independent certified public accountants in form and substance as is customarily given by independent certified public accountants to underwriters in an underwritten public offering, addressed to the Investors, and (ii) an
opinion, dated as of such date, of counsel representing the Company for purposes of such Registration Statement, in form, scope and substance as is customarily given in an underwritten public offering, addressed to the Investors. 

(g) If any Investor may be required under applicable securities law to be described in any Registration Statement as an underwriter and
such Investor consents to so being named an underwriter, upon the written request of such Investor, the Company shall make available for inspection by (i) such Investor, (ii) legal counsel for such Investor and (iii) one (1) firm
of accountants or other agents retained by such Investor (collectively, the “Inspectors”), all pertinent financial and other records, and pertinent corporate documents and properties of the Company (collectively, the
“Records”), as shall be reasonably deemed necessary by each Inspector, and cause the Company’s officers, directors and employees to supply all information which any Inspector may reasonably request; provided, however, each
Inspector shall agree in writing to hold in strict confidence and not to make any disclosure (except to such Investor) or use of any Record or other information which the Company’s board of directors determines in good faith to be confidential,
and of which determination the Inspectors are so notified, unless (1) the disclosure of such Records is necessary to avoid or correct a misstatement or omission in any Registration Statement or is otherwise required under the 1933 Act,
(2) the release of such Records is ordered pursuant to a final, non-appealable subpoena or order from a court or government body of competent jurisdiction, or (3) the information in such Records has been made generally available to the
public other than by disclosure in violation of this Agreement or any other Transaction Document (as defined in the Securities Purchase Agreements). Such Investor agrees that it shall, upon learning that disclosure of such Records is sought in or by
a court or governmental body of competent jurisdiction or through other means, give prompt notice to the Company and allow the Company, at its expense, to undertake appropriate action to prevent disclosure of, or to obtain a protective order for,
the Records deemed confidential. Nothing herein (or in any other confidentiality agreement between the Company and such Investor, if any) shall be deemed to limit any Investor’s ability to sell Registrable Securities in a manner which is
otherwise consistent with applicable laws and regulations. 
 (h) The Company shall hold in confidence and not make any
disclosure of information concerning an Investor provided to the Company unless (i) disclosure of such information is necessary to comply with federal or state securities laws, (ii) the disclosure of such information is necessary to avoid
or correct a misstatement or omission in any Registration Statement or is otherwise required to be disclosed in such Registration Statement pursuant to the 1933 Act, (iii) the release of such information is ordered pursuant to a subpoena or
other final, non-appealable order from a court or governmental body of competent jurisdiction, or (iv) such information has been made generally available to the public other than by disclosure in violation of this Agreement or any other
Transaction Document. The Company agrees that it shall, upon learning that disclosure of such information concerning an Investor is sought in or by a court or governmental body of competent jurisdiction or through other means, give prompt written
notice to such Investor and allow such Investor, at such Investor’s expense, to undertake appropriate action to prevent disclosure of, or to obtain a protective order for, such information. 

  
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 (i) Without limiting any obligation of the Company under the Securities Purchase Agreements,
the Company shall use commercially reasonable efforts either to (i) cause all of the Registrable Securities covered by each Registration Statement to be listed on each securities exchange on which securities of the same class or series issued
by the Company are then listed, if any, if the listing of such Registrable Securities is then permitted under the rules of such exchange, (ii) secure designation and quotation of all of the Registrable Securities covered by each Registration
Statement on the OTC Bulletin Board, or (iii) if, despite the Company’s commercially reasonable efforts to satisfy the preceding clauses (i) or (ii) the Company is unsuccessful in satisfying the preceding clauses (i) or
(ii), without limiting the generality of the foregoing, to use commercially reasonable efforts to arrange for at least two market makers to register with the Financial Industry Regulatory Authority (“FINRA”) as such with respect to
such Registrable Securities. In addition, the Company shall cooperate with each Investor and any broker or dealer through which any such Investor proposes to sell its Registrable Securities in effecting a filing with FINRA pursuant to FINRA Rule
5110 as requested by such Investor. The Company shall pay all fees and expenses in connection with satisfying its obligations under this Section 3(i). 
 (j) The Company shall cooperate with the Investors who hold Registrable Securities being offered and, to the extent applicable, facilitate the timely preparation and delivery of certificates (not bearing
any restrictive legend) representing the Registrable Securities to be offered pursuant to a Registration Statement and enable such certificates to be in such denominations or amounts (as the case may be) as the Investors may reasonably request from
time to time and registered in such names as the Investors may request. 
 (k) If requested by an Investor, the Company shall as
soon as practicable after receipt of notice from such Investor and subject to Section 3(p) hereof, (i) incorporate in a prospectus supplement or post-effective amendment such information as an Investor reasonably requests to be included
therein relating to the sale and distribution of Registrable Securities, including, without limitation, information with respect to the number of Registrable Securities being offered or sold, the purchase price being paid therefor and any other
terms of the offering of the Registrable Securities to be sold in such offering; (ii) make all required filings of such prospectus supplement or post-effective amendment after being notified of the matters to be incorporated in such prospectus
supplement or post-effective amendment; and (iii) supplement or make amendments to any Registration Statement or prospectus contained therein if reasonably requested by an Investor holding any Registrable Securities. 

(l) The Company shall use commercially reasonable efforts to cause the Registrable Securities covered by a Registration Statement to be
registered with or approved by such other governmental agencies or authorities as may be necessary to consummate the disposition of such Registrable Securities. 
 (m) The Company shall make generally available to its security holders as soon as practical, but not later than ninety (90) days after the close of the period covered thereby, an earnings statement
(in form complying with, and in the manner provided by, the provisions of Rule 158 under the 1933 Act) covering a twelve-month period beginning not later than the first day of the Company’s fiscal quarter next following the applicable Effective
Date of each Registration Statement. 

  
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 (n) The Company shall otherwise use commercially reasonable efforts to comply with all
applicable rules and regulations of the SEC in connection with any registration hereunder. 
 (o) Within one (1) Business
Day after a Registration Statement which covers Registrable Securities is declared effective by the SEC, the Company shall deliver, and shall cause legal counsel for the Company to deliver, to the transfer agent for such Registrable Securities (with
copies to the Investors whose Registrable Securities are included in such Registration Statement) confirmation that such Registration Statement has been declared effective by the SEC in the form attached hereto as Exhibit A.

 (p) Notwithstanding anything to the contrary herein (but subject to the last sentence of this Section 3(p)), at any time
after the Effective Date of a particular Registration Statement, the Company may delay the disclosure of material, non-public information concerning the Company or any of its Subsidiaries the disclosure of which at the time is not, in the good faith
opinion of the board of directors of the Company, in the best interest of the Company and, in the opinion of counsel to the Company, otherwise required (a “Grace Period”), provided that the Company shall promptly notify the
Investors in writing of the (i) existence of material, non-public information giving rise to a Grace Period (provided that in each such notice the Company shall not disclose the content of such material, non-public information to any of the
Investors) and the date on which such Grace Period will begin and (ii) date on which such Grace Period ends, provided further that (I) no Grace Period shall exceed fifteen (15) consecutive Trading Days and during any three hundred
sixty five (365) day period all such Grace Periods shall not exceed an aggregate of forty (40) Trading Days, and (II) the first day of any Grace Period must be at least five (5) Trading Days after the last day of any prior Grace
Period (each, an “Allowable Grace Period”). For purposes of determining the length of a Grace Period above, such Grace Period shall begin on and include the date the Investors receive the notice referred to in clause (i) above
and shall end on and include the later of the date the Investors receive the notice referred to in clause (ii) above and the date referred to in such notice. The provisions of Section 3(e) hereof shall not be applicable during the period
of any Allowable Grace Period. Upon expiration of each Grace Period, the Company shall again be bound by the first sentence of Section 3(d) with respect to the information giving rise thereto unless such material, non-public information is no
longer applicable. Notwithstanding anything to the contrary contained in this Section 3(p), the Company shall cause its transfer agent to deliver unlegended shares of Common Stock to a transferee of an Investor in accordance with the terms of
the Securities Purchase Agreements in connection with any sale of Registrable Securities with respect to which such Investor has entered into a contract for sale, and delivered a copy of the prospectus included as part of the particular Registration
Statement to the extent applicable, prior to such Investor’s receipt of the notice of a Grace Period and for which the Investor has not yet settled. 
 (q) The Company shall use commercially reasonable efforts to maintain eligibility for use of Form S-3 (or any successor form thereto) for the registration of the resale of all the Registrable Securities.

  

	4.	Obligations of the Investors. 

 (a) At least three (3) Business Days prior to the first anticipated filing date of each Registration Statement, the Company shall notify each Investor in writing of the information the

  
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Company requires from each such Investor with respect to such Registration Statement. It shall be a condition precedent to the obligations of the Company to complete the registration pursuant to
this Agreement with respect to the Registrable Securities (and the timing therefor) of a particular Investor that such Investor shall furnish to the Company such information regarding itself, the Registrable Securities held by it and the intended
method of disposition of the Registrable Securities held by it, as shall be reasonably required to effect and maintain the effectiveness of the registration of such Registrable Securities and shall execute such documents in connection with such
registration as the Company may reasonably request. 
 (b) Each Investor, by such Investor’s acceptance of the Registrable
Securities, agrees to cooperate with the Company as reasonably requested by the Company in connection with the preparation and filing of each Registration Statement hereunder, unless such Investor has notified the Company in writing of such
Investor’s election to exclude all of such Investor’s Registrable Securities from such Registration Statement. 
 (c)
Each Investor agrees that, upon receipt of any notice from the Company of the happening of any event of the kind described in Section 3(e) or the first sentence of 3(d) (including the existence of a Grace Period), such Investor will immediately
discontinue disposition of Registrable Securities pursuant to any Registration Statement(s) covering such Registrable Securities until such Investor’s receipt of the copies of the supplemented or amended prospectus contemplated by
Section 3(e) or the first sentence of Section 3(d) or receipt of notice that no supplement or amendment is required. Notwithstanding anything to the contrary in this Section 4(c), the Company shall cause its transfer agent to deliver
unlegended shares of Common Stock to a transferee of an Investor in accordance with the terms of the Securities Purchase Agreements in connection with any sale of Registrable Securities with respect to which such Investor has entered into a contract
for sale prior to the Investor’s receipt of a notice from the Company of the happening of any event of the kind described in Section 3(e) or the first sentence of Section 3(d) and for which such Investor has not yet settled.

 (d) Each Investor covenants and agrees that it will comply with the prospectus delivery requirements of the 1933 Act as
applicable to it in connection with sales of Registrable Securities pursuant to a Registration Statement. 
  

	5.	Expenses of Registration. 

All reasonable expenses, other than underwriting discounts and commissions, incurred in connection with registrations, filings or
qualifications pursuant to Sections 2 and 3, including, without limitation, all registration, listing and qualifications fees, printers and accounting fees, FINRA filing fees (if any) and fees and disbursements of counsel for the Company shall be
paid by the Company. 
  

	6.	Indemnification. 

 (a) To
the fullest extent permitted by law, the Company will, and hereby does, indemnify, hold harmless and defend each Investor and each of its directors, officers, shareholders, members, partners, employees, agents, advisors, representatives (and any
other Persons with a functionally equivalent role of a Person holding such titles notwithstanding the 

  
 11 

 
lack of such title or any other title) and each Person, if any, who controls such Investor within the meaning of the 1933 Act or the 1934 Act and each of the directors, officers, shareholders,
members, partners, employees, agents, advisors, representatives (and any other Persons with a functionally equivalent role of a Person holding such titles notwithstanding the lack of such title or any other title) of such controlling Persons (each,
an “Indemnified Person”), against any claims, damages, liabilities, judgments, fines, penalties, charges, costs (including, without limitation, court costs, reasonable attorneys’ fees and costs of defense and investigation),
amounts paid in settlement or expenses, joint or several, (collectively, “Claims”) incurred in defending any action, claim, suit, inquiry, proceeding, investigation or appeal taken from the foregoing by or before any court or
governmental, administrative or other regulatory agency, body or the SEC, (“Indemnified Damages”), to which any of them may become subject insofar as such Claims arise out of or are based upon: (i) any untrue statement or
alleged untrue statement of a material fact in a Registration Statement or any post-effective amendment thereto, or the omission or alleged omission to state a material fact required to be stated therein or necessary to make the statements therein
not misleading, (ii) any untrue statement or alleged untrue statement of a material fact contained in any preliminary prospectus if used prior to the effective date of such Registration Statement, or contained in the final prospectus (as
amended or supplemented, if the Company files any amendment thereof or supplement thereto with the SEC) or the omission or alleged omission to state therein any material fact necessary to make the statements made therein, in light of the
circumstances under which the statements therein were made, not misleading or (iii) any violation or alleged violation by the Company of the 1933 Act, the 1934 Act, any other law, including, without limitation, any state securities law, or any
rule or regulation thereunder relating to the offer or sale of the Registrable Securities pursuant to a Registration Statement (the matters in the foregoing clauses (i) through (iii) being, collectively, “Violations”).
Subject to Section 6(c), the Company shall reimburse the Indemnified Persons, promptly as such expenses are incurred and are due and payable, for any legal fees or other reasonable expenses incurred by them in connection with investigating or
defending any such Claim. Notwithstanding anything to the contrary contained herein, the indemnification agreement contained in this Section 6(a): (1) shall not apply to a Claim by an Indemnified Person arising out of or based upon a
Violation which occurs in reliance upon and in conformity with information furnished to the Company by such Indemnified Person for use in connection with the preparation of such Registration Statement or any such amendment thereof or supplement
thereto; (2) shall not be available to a particular Indemnified Person to the extent such Claim is based on a failure of such Indemnified Person or its affiliates to timely deliver or to cause to be timely delivered the prospectus made
available by the Company (to the extent applicable), including, without limitation, a corrected prospectus, if such prospectus or corrected prospectus was timely made available by the Company pursuant to Section 3(c) and then only if, and to
the extent that, following the receipt of the corrected prospectus no grounds for such Claim would have existed; (3) shall not be available to a particular Investor or its affiliates with respect to a particular sale by such Investor of
Registrable Securities pursuant to a Registration Statement only if such sale was made by such Investor in violation of its obligations under Section 4(c) of this Agreement; and (4) shall not apply to amounts paid in settlement of any
Claim if such settlement is effected without the prior written consent of the Company, which consent shall not be unreasonably withheld or delayed. Such indemnity shall remain in full force and effect regardless of any investigation made by or on
behalf of the Indemnified Person and shall survive the transfer of any of the Registrable Securities by any of the Investors pursuant to Section 9. 

  
 12 

 (b) In connection with any Registration Statement in which an Investor is participating,
such Investor agrees to severally and not jointly indemnify, hold harmless and defend, to the same extent and in the same manner as is set forth in Section 6(a), the Company, each of its directors, each of its officers and each Person, if any,
who controls the Company within the meaning of the 1933 Act or the 1934 Act (each, an “Indemnified Party”), against any Claim or Indemnified Damages to which any of them may become subject, under the 1933 Act, the 1934 Act or
otherwise, insofar as such Claim or Indemnified Damages arise out of or are based upon any Violation, in each case, to the extent, and only to the extent, that such Violation occurs in reliance upon and in conformity with information furnished to
the Company by such Investor expressly for use in connection with such Registration Statement; and, subject to Section 6(c) and the below provisos in this Section 6(b), such Investor will reimburse an Indemnified Party any legal or other
expenses reasonably incurred by such Indemnified Party in connection with defending any such Claim; provided, however, the indemnity agreement contained in this Section 6(b) and the agreement with respect to contribution contained in
Section 7 shall not apply to amounts paid in settlement of any Claim if such settlement is effected without the prior written consent of such Investor, which consent shall not be unreasonably withheld or delayed, provided further that such
Investor shall be liable under this Section 6(b) for only that amount of a Claim or Indemnified Damages as does not exceed the net proceeds to such Investor as a result of the applicable sale of Registrable Securities pursuant to such
Registration Statement. Such indemnity shall remain in full force and effect regardless of any investigation made by or on behalf of such Indemnified Party and shall survive the transfer of any of the Registrable Securities by any of the Investors
pursuant to Section 9. 
 (c) Promptly after receipt by an Indemnified Person or Indemnified Party (as the case may be)
under this Section 6 of notice of the commencement of any action or proceeding (including, without limitation, any governmental action or proceeding) involving a Claim, such Indemnified Person or Indemnified Party (as the case may be) shall, if
a Claim in respect thereof is to be made against any indemnifying party under this Section 6, deliver to the indemnifying party a written notice of the commencement thereof, and the indemnifying party shall have the right to participate in,
and, to the extent the indemnifying party so desires, jointly with any other indemnifying party similarly noticed, to assume control of the defense thereof with counsel mutually satisfactory to the indemnifying party and the Indemnified Person or
the Indemnified Party (as the case may be); provided, however, an Indemnified Person or Indemnified Party (as the case may be) shall have the right to retain its own counsel with the fees and expenses of such counsel to be paid by the indemnifying
party if: (i) the indemnifying party has agreed in writing to pay such fees and expenses; (ii) the indemnifying party shall have failed promptly to assume the defense of such Claim and to employ counsel reasonably satisfactory to such
Indemnified Person or Indemnified Party (as the case may be) in any such Claim; or (iii) the named parties to any such Claim (including, without limitation, any impleaded parties) include both such Indemnified Person or Indemnified Party (as
the case may be) and the indemnifying party, and such Indemnified Person or such Indemnified Party (as the case may be) shall have been advised by counsel that a conflict of interest is likely to exist if the same counsel were to represent such
Indemnified Person or such Indemnified Party and the indemnifying party, in which case, if such Indemnified Person or such Indemnified Party (as the case may be) notifies the indemnifying party in writing that it elects to employ separate counsel at
the expense of the indemnifying party, then the indemnifying party shall not have the right to assume the defense thereof and such counsel shall be at the expense of the Indemnifying Party, provided further that in the case of

  
 13 

 
clause (iii) above the indemnifying party shall not be responsible for the reasonable fees and expenses of more than one (1) separate legal counsel for such Indemnified Person or
Indemnified Party (as the case may be). The Indemnified Party or Indemnified Person (as the case may be) shall reasonably cooperate with the indemnifying party in connection with any negotiation or defense of any such action or Claim by the
indemnifying party and shall furnish to the indemnifying party all information reasonably available to the Indemnified Party or Indemnified Person (as the case may be) which relates to such action or Claim. The indemnifying party shall keep the
Indemnified Party or Indemnified Person (as the case may be) reasonably apprised at all times as to the status of the defense or any settlement negotiations with respect thereto. No indemnifying party shall be liable for any settlement of any
action, claim or proceeding effected without its prior written consent; provided, however, the indemnifying party shall not unreasonably withhold, delay or condition its consent. No indemnifying party shall, without the prior written consent of the
Indemnified Party or Indemnified Person (as the case may be), consent to entry of any judgment or enter into any settlement or other compromise which does not include as an unconditional term thereof the giving by the claimant or plaintiff to such
Indemnified Party or Indemnified Person (as the case may be) of a release from all liability in respect to such Claim or litigation, and such settlement shall not include any admission as to fault on the part of the Indemnified Party. Following
indemnification as provided for hereunder, the indemnifying party shall be subrogated to all rights of the Indemnified Party or Indemnified Person (as the case may be) with respect to all third parties, firms or corporations relating to the matter
for which indemnification has been made. The failure to deliver written notice to the indemnifying party within a reasonable time of the commencement of any such action shall not relieve such indemnifying party of any liability to the Indemnified
Person or Indemnified Party (as the case may be) under this Section 6, except to the extent that the indemnifying party is materially and adversely prejudiced in its ability to defend such action. 

(d) No Person involved in the sale of Registrable Securities who is guilty of fraudulent misrepresentation (within the meaning of
Section 11(f) of the 1933 Act) in connection with such sale shall be entitled to indemnification from any Person involved in such sale of Registrable Securities who is not guilty of fraudulent misrepresentation. 

(e) The indemnification required by this Section 6 shall be made by periodic payments of the amount thereof during the course of the
investigation or defense, as and when bills are received or Indemnified Damages are incurred. 
 (f) The indemnity and
contribution agreements contained herein shall be in addition to (i) any cause of action or similar right of the Indemnified Party or Indemnified Person against the indemnifying party or others, and (ii) any liabilities the indemnifying
party may be subject to pursuant to the law. 
  

	7.	Contribution. 

 To the
extent any indemnification by an indemnifying party is prohibited or limited by law, the indemnifying party agrees to make the maximum contribution with respect to any amounts for which it would otherwise be liable under Section 6 to the
fullest extent permitted by law; provided, however: (i) no contribution shall be made under circumstances where the maker would not have been liable for indemnification under the fault standards set

  
 14 

 
forth in Section 6 of this Agreement, (ii) no Person involved in the sale of Registrable Securities which Person is guilty of fraudulent misrepresentation (within the meaning of
Section 11(f) of the 1933 Act) in connection with such sale shall be entitled to contribution from any Person involved in such sale of Registrable Securities who was not guilty of fraudulent misrepresentation; and (iii) contribution by any
seller of Registrable Securities shall be limited in amount to the amount of net proceeds received by such seller from the applicable sale of such Registrable Securities pursuant to such Registration Statement. Notwithstanding the provisions of this
Section 7, no Investor shall be required to contribute, in the aggregate, any amount in excess of the amount by which the net proceeds actually received by such Investor from the applicable sale of the Registrable Securities subject to the
Claim exceeds the amount of any damages that such Investor has otherwise been required to pay, or would otherwise be required to pay under Section 6(b), by reason of such untrue or alleged untrue statement or omission or alleged omission.

  

	8.	Reports Under the 1934 Act. 

 With a view to making available to the Investors the benefits of Rule 144, the Company agrees to: 
 (a) make and keep public information available, as those terms are understood and defined in Rule 144; 
 (b) file with the SEC in a timely manner all reports and other documents required of the Company under the 1933 Act and the 1934 Act so long as the Company remains subject to such requirements (it being
understood and agreed that nothing herein shall limit any obligations of the Company under the Securities Purchase Agreements) and the filing of such reports and other documents is required for the applicable provisions of Rule 144; and 

(c) furnish to each Investor so long as such Investor owns Registrable Securities, promptly upon request, (i) a written statement by
the Company, if true, that it has complied with the reporting, submission and posting requirements of Rule 144 and the 1934 Act, (ii) a copy of the most recent annual or quarterly report of the Company and such other reports and documents so
filed by the Company with the SEC if such reports are not publicly available via EDGAR, and (iii) such other information as may be reasonably requested to permit the Investors to sell such securities pursuant to Rule 144 without registration.

  

	9.	Assignment of Registration Rights. 

 All or any portion of the rights under this Agreement shall be assignable by each Investor to any transferee or assignee (as the case may be) of all or any portion of such Investor’s Registrable
Securities or Warrants, with the Company’s reasonable consent, if: (i) such Investor agrees in writing with such transferee or assignee (as the case may be) to assign all or any portion of such rights, and a copy of such agreement is
furnished to the Company within a reasonable time after such transfer or assignment (as the case may be); (ii) the Company is, within a reasonable time after such transfer or assignment (as the case may be), furnished with written notice of
(a) the name and address of such transferee or assignee (as the case may be), and (b) the securities with respect to which such registration rights are being transferred or 

  
 15 

 
assigned (as the case may be); (iii) immediately following such transfer or assignment (as the case may be) the further disposition of such securities by such transferee or assignee (as the
case may be) is restricted under the 1933 Act or applicable state securities laws if so required; (iv) at or before the time the Company receives the written notice contemplated by clause (ii) of this sentence such transferee or assignee
(as the case may be) agrees in writing with the Company to be bound by all of the provisions contained herein; (v) such transfer or assignment (as the case may be) shall have been made in accordance with the applicable requirements of the
applicable Securities Purchase Agreement and the Warrants (as the case may be); and (vi) such transfer or assignment (as the case may be) shall have been conducted in accordance with all applicable federal and state securities laws. 

 

	10.	Amendment of Registration Rights. 

 Provisions of this Agreement may be amended only with the written consent of the Company and the Required Investors. Any amendment effected in accordance with this Section 10 shall be binding upon
each Investor and the Company, provided that no such amendment shall be effective to the extent that it (a) applies to less than all of the holders of Registrable Securities, (b) imposes any obligation or liability on any Investor without
such Investor’s prior written consent (which may be granted or withheld in such Investor’s sole discretion) or (c) applies retroactively. No waiver shall be effective unless it is in writing and signed by an authorized representative
of the waiving party, provided that the Required Investors (in a writing signed by all of the Required Investors) may waive any provision of this Agreement, and any waiver of any provision of this Agreement made in conformity with the provisions of
this Section 10 shall be binding on each Investor, provided that no such waiver shall be effective to the extent that it (1) applies to less than all the Investors (unless a party gives a waiver as to itself only) or (2) imposes any
obligation or liability on any Investor without such Investor’s prior written consent (which may be granted or withheld in such Investor’s sole discretion). No consideration shall be offered or paid to any Person to amend or consent to a
waiver or modification of any provision of this Agreement unless the same consideration also is offered to all of the parties to this Agreement. 
  

	11.	Miscellaneous. 

 (a)
Solely for purposes of this Agreement, a Person is deemed to be a holder of Registrable Securities whenever such Person owns, or is deemed to own, of record such Registrable Securities. If the Company receives conflicting instructions, notices or
elections from two or more Persons with respect to the same Registrable Securities, the Company shall act upon the basis of instructions, notice or election received from such record owner of such Registrable Securities. 

  
 16 

 (b) Any notices, consents, waivers or other communications required or permitted to be given
under the terms of this Agreement must be in writing and will be deemed to have been delivered: (i) upon receipt, when delivered personally; (ii) upon receipt, when sent by facsimile (provided confirmation of transmission is mechanically
or electronically generated and kept on file by the sending party); (iii) by electronic mail (provided confirmation of transmission is electronically generated and kept on file by the sending party); or (iv) one (1) Business Day after
deposit with a nationally recognized overnight delivery service with next day delivery specified, in each case, properly addressed to the party to receive the same. The addresses and facsimile numbers for such communications shall be: 

If to the Company: 
 ARCA biopharma, Inc. 
 8001 Arista Place, Suite 430 

Broomfield, Colorado 80021 
 E-mail: pat.wheeler@arcabiopharma.com 
 Facsimile:  (720) 940-2457

 Attention:  Chief Financial Officer 
 With a copy (for informational purposes only) to: 
 Cooley LLP 

380 Interlocken Crescent, Suite 900 
 Broomfield, CO 80021 
 E-mail: fassettbd@cooley.com 

Facsimile:  (720) 566-4099 
 Attention:  Brent D. Fassett 
 If to the Transfer Agent: 

Computershare Trust Company, N.A. 
 350 Indiana Street, Suite 800 
 Golden, CO 80401 

E-mail: kathy.kinard@computershare.com 
 Facsimile:  (303) 262-0632 
 Attention:  Kathy Kinard

 If to a Buyer, to its address, facsimile number or electronic mail address (as the case may be) set forth on such Buyer’s signature page
to its Securities Purchase Agreement, or to such other address and/or facsimile number and/or to the attention of such other Person as the recipient party has specified by written notice given to each other party five (5) days prior to the
effectiveness of such change. Written confirmation of receipt (A) given by the recipient of such notice, consent, waiver or other communication, (B) mechanically or electronically generated by the sender’s facsimile machine or
electronic mail transmission containing the time, date and recipient facsimile number or electronic mail address or (C) provided by a courier or overnight courier service shall be rebuttable evidence of personal service, receipt by facsimile or
receipt from a nationally recognized overnight delivery service in accordance with clause (i), (ii) or (iii) above, respectively. 
 (c) Failure of any party to exercise any right or remedy under this Agreement or otherwise, or delay by a party in exercising such right or remedy, shall not operate as a waiver thereof. The Company and
each Investor acknowledge and agree that irreparable damage would 

  
 17 

 
occur in the event that any of the provisions of this Agreement were not performed in accordance with their specific terms or were otherwise breached. It is accordingly agreed that each party
hereto shall be entitled to an injunction or injunctions to prevent or cure breaches of the provisions of this Agreement by any other party hereto and to enforce specifically the terms and provisions hereof (without the necessity of showing economic
loss and without any bond or other security being required), this being in addition to any other remedy to which any party may be entitled by law or equity. 
 (d) All questions concerning the construction, validity, enforcement and interpretation of this Agreement shall be governed by the internal laws of the State of New York, without giving effect to any
choice of law or conflict of law provision or rule (whether of the State of New York or any other jurisdictions) that would cause the application of the laws of any jurisdictions other than the State of New York. Each party hereby irrevocably
submits to the exclusive jurisdiction of the state and federal courts sitting in The City of New York, Borough of Manhattan, for the adjudication of any dispute hereunder or in connection herewith or with any transaction contemplated hereby or
discussed herein, and hereby irrevocably waives, and agrees not to assert in any suit, action or proceeding, any claim that it is not personally subject to the jurisdiction of any such court, that such suit, action or proceeding is brought in an
inconvenient forum or that the venue of such suit, action or proceeding is improper. Each party hereby irrevocably waives personal service of process and consents to process being served in any such suit, action or proceeding by mailing a copy
thereof to such party at the address for such notices to it under this Agreement and agrees that such service shall constitute good and sufficient service of process and notice thereof. Nothing contained herein shall be deemed to limit in any way
any right to serve process in any manner permitted by law. If any provision of this Agreement shall be invalid or unenforceable in any jurisdiction, such invalidity or unenforceability shall not affect the validity or enforceability of the remainder
of this Agreement in that jurisdiction or the validity or enforceability of any provision of this Agreement in any other jurisdiction. EACH PARTY HEREBY IRREVOCABLY WAIVES ANY RIGHT IT MAY HAVE TO, AND AGREES NOT TO REQUEST, A JURY TRIAL FOR THE
ADJUDICATION OF ANY DISPUTE HEREUNDER OR IN CONNECTION HEREWITH OR ARISING OUT OF THIS AGREEMENT OR ANY TRANSACTION CONTEMPLATED HEREBY. 
 (e) This Agreement, the other Transaction Documents, the schedules and exhibits attached hereto and thereto and the instruments referenced herein and therein constitute the entire agreement among the
parties hereto and thereto solely with respect to the subject matter hereof and thereof. There are no restrictions, promises, warranties or undertakings, other than those set forth or referred to herein and therein. This Agreement, the other
Transaction Documents, the schedules and exhibits attached hereto and thereto and the instruments referenced herein and therein supersede all prior agreements and understandings among the parties hereto solely with respect to the subject matter
hereof and thereof. 
 (f) Subject to compliance with Section 9 (if applicable), this Agreement shall inure to the benefit
of and be binding upon the permitted successors and assigns of each of the parties hereto. This Agreement is not for the benefit of, nor may any provision hereof be enforced by, any Person, other than the parties hereto, their respective permitted
successors and assigns and the Persons referred to in Sections 6 and 7 hereof. 

  
 18 

 (g) The headings in this Agreement are for convenience of reference only and shall not limit
or otherwise affect the meaning hereof. Unless the context clearly indicates otherwise, each pronoun herein shall be deemed to include the masculine, feminine, neuter, singular and plural forms thereof. The terms “including,”
“includes,” “include” and words of like import shall be construed broadly as if followed by the words “without limitation.” The terms “herein,” “hereunder,” “hereof” and words of like
import refer to this entire Agreement instead of just the provision in which they are found. 
 (h) This Agreement may be
executed in two or more counterparts, all of which shall be considered one and the same agreement and shall become effective when counterparts have been signed by each party and delivered to the other party. In the event that any signature is
delivered by facsimile transmission or by an e-mail which contains a portable document format (.pdf) file of an executed signature page, such signature page shall create a valid and binding obligation of the party executing (or on whose behalf such
signature is executed) with the same force and effect as if such signature page were an original thereof. 
 (i) Each party
shall do and perform, or cause to be done and performed, all such further acts and things, and shall execute and deliver all such other agreements, certificates, instruments and documents as any other party may reasonably request in order to carry
out the intent and accomplish the purposes of this Agreement and the consummation of the transactions contemplated hereby. 

(j) The language used in this Agreement will be deemed to be the language chosen by the parties to express their mutual intent and no
rules of strict construction will be applied against any party. Notwithstanding anything to the contrary set forth in Section 10, terms used in this Agreement but defined in the other Transaction Documents shall have the meanings ascribed to
such terms on the Closing Date in such other Transaction Documents unless otherwise consented to in writing by each Investor. 

[signature pages follow] 

  
 19 

 IN WITNESS WHEREOF, Buyer and the Company have caused their respective signature page
to this Registration Rights Agreement to be duly executed as of the date first written above. 
  

			
	COMPANY:
	
	ARCA BIOPHARMA INC.
		
	By:	 	  

		 	Patrick M. Wheeler, Chief Financial Officer

 IN WITNESS WHEREOF, Buyer and the Company have caused their respective signature page
to this Registration Rights Agreement to be duly executed as of the date first written above. 
  

			
	BUYER:
	
	[                           
             ]
		
	By:	 	  

	Its:	 	  

	
	  

	By:	 	  

	Its:	 	  

 EXHIBIT A 
 FORM OF NOTICE OF EFFECTIVENESS 
 OF REGISTRATION STATEMENT

             , 20    

 Ladies and Gentlemen: 
 Reference is made to the Subscription Agreement (the “Securities Purchase Agreement”) entered into by and between ARCA biopharma, Inc. (the “Company”) and the buyer named
therein ( the “Holder”) pursuant to which the Company issued to the Holder shares of the Company’s common stock, $0.001 par value per share (the “Common Stock”), and warrants exercisable for shares of
Common Stock (the “Warrants”). Pursuant to the Securities Purchase Agreement, the Company also has entered into a Registration Rights Agreement with the Holder (the “Registration Rights Agreement”) pursuant to which
the Company agreed, among other things, to register the Registrable Securities (as defined in the Registration Rights Agreement), including the shares of Common Stock issuable upon exercise of the Warrants, under the Securities Act of 1933, as
amended (the “1933 Act”). In connection with the Company’s obligations under the Registration Rights Agreement, on                  ,
20    , the Company filed a Registration Statement on Form S-3 (File No. 333-            ) (the “Registration Statement”) with the Securities and
Exchange Commission (the “SEC”) relating to the Registrable Securities which names the Holder as a selling stockholder thereunder. 
 In connection with the foregoing, we advise you that a member of the SEC’s staff has advised us by telephone that the SEC has entered an order declaring the Registration Statement effective under the
1933 Act at [ENTER TIME OF EFFECTIVENESS] on [ENTER DATE OF EFFECTIVENESS]. 
  

			
	Very truly yours,
	
	COOLEY LLP
		
	By:	 	  

  

			
	cc:	  	ARCA biopharma, Inc.
		  	[LIST NAMES OF HOLDERS]

 EXHIBIT B 
 SELLING STOCKHOLDERS 
 The shares of common stock being offered by the
selling stockholders are those issued to the selling stockholders and those issuable to the selling stockholders upon exercise of the warrants. For additional information regarding the issuance of the common stock and the warrants, see “Private
Placement of Common Stock and Warrants” above. We are registering the shares of common stock in order to permit the selling stockholders to offer the shares for resale from time to time. Except for the ownership of the common stock and the
warrants issued pursuant to (i) the Subscription Agreements and (ii) the Subscription Agreements entered into on             , 2012, the selling stockholders have not had any
material relationship with us within the past three years. 
 The table below lists the selling stockholders and other
information regarding the beneficial ownership (as determined under Section 13(d) of the Securities Exchange Act of 1934, as amended, and the rules and regulations thereunder) of the shares of common stock held by each of the selling
stockholders. The second column lists the number of shares of common stock beneficially owned by the selling stockholders, based on their respective ownership of shares of common stock and warrants, as of
            , 20    , assuming exercise of the warrants held by each such selling stockholder on that date but taking account of any limitations on exercise set forth
therein. 
 The third column lists the shares of common stock being offered by this prospectus by the selling stockholders and
does not take into account any limitations on exercise of the warrants set forth therein. 
 In accordance with the terms of a
registration rights agreement with the holders of the common stock and the warrants, this prospectus generally covers the resale of the sum of (i) the shares of common stock issued to the selling stockholders and (ii) the maximum number of
shares of common stock issuable upon exercise of the warrants determined as if the outstanding warrants were exercised in full (without regard to any limitations on exercise contained therein) as of the trading day immediately preceding the date
this registration statement was initially filed with the SEC. Because the exercise price of the warrants may be adjusted, the number of shares that will actually be issued may be more or less than the number of shares being offered by this
prospectus. The fourth column assumes the sale of all of the shares offered by the selling stockholders pursuant to this prospectus. 
 Under the terms of the warrants, a selling stockholder may not exercise the warrants to the extent (but only to the extent) such selling stockholder or any of its affiliates would beneficially own a
number of shares of our common stock which would exceed 4.9%. The beneficial ownership limitation under the warrants will not apply if the holder beneficially owned, immediately following the issuance of such warrants, in excess of 4.9% of the
shares of common stock then outstanding. The number of shares in the second column reflects these limitations. The selling stockholders may sell all, some or none of their shares in this offering. See “Plan of Distribution.” 

							
	 Name of Selling Stockholder
	  	Number of Shares of
Common Stock Owned
Prior to Offering	  	Maximum Number of
Shares of Common Stock to
be Sold Pursuant to
this
Prospectus	  	Number of Shares of
Common Stock Owned
After Offering
		  		  		  	
		  		  		  	
		  		  		  	
		  		  		  	
		  		  		  	

 PLAN OF DISTRIBUTION 

We are registering the shares of common stock issued to the selling stockholders and the shares of common stock issuable upon exercise of
the warrants to permit the resale of these shares of common stock by the selling stockholders from time to time after the date of this prospectus. We will not receive any of the proceeds from the sale by the selling stockholders of the shares of
common stock. We will bear all fees and expenses incident to our obligation to register the shares of common stock. 
 The
selling stockholders may sell all or a portion of the shares of common stock held by them and offered hereby from time to time directly or through one or more underwriters, broker-dealers or agents. If the shares of common stock are sold through
underwriters or broker-dealers, the selling stockholders will be responsible for underwriting discounts or commissions or agent’s commissions. The shares of common stock may be sold in one or more transactions at fixed prices, at prevailing
market prices at the time of the sale, at varying prices determined at the time of sale or at negotiated prices. These sales may be effected in transactions, which may involve crosses or block transactions, pursuant to one or more of the following
methods: 
  

	 	•	 	 on any national securities exchange or quotation service on which the securities may be listed or quoted at the time of sale;

  

	 	•	 	 in the over-the-counter market; 

  

	 	•	 	 in transactions otherwise than on these exchanges or systems or in the over-the-counter market; 

 

	 	•	 	 through the writing or settlement of options, whether such options are listed on an options exchange or otherwise; 

 

	 	•	 	 ordinary brokerage transactions and transactions in which the broker-dealer solicits purchasers; 

 

	 	•	 	 block trades in which the broker-dealer will attempt to sell the shares as agent but may position and resell a portion of the block as principal to
facilitate the transaction; 

  

	 	•	 	 purchases by a broker-dealer as principal and resale by the broker-dealer for its account; 

 

	 	•	 	 an exchange distribution in accordance with the rules of the applicable exchange; 

 

	 	•	 	 privately negotiated transactions; 

  

	 	•	 	 short sales made after the date the Registration Statement is declared effective by the SEC; 

 

	 	•	 	 broker-dealers may agree with a selling securityholder to sell a specified number of such shares at a stipulated price per share;

	 	•	 	 a combination of any such methods of sale; and 

  

	 	•	 	 any other method permitted pursuant to applicable law. 

 The selling stockholders may also sell shares of common stock under Rule 144 promulgated under the Securities Act of 1933, as amended, if available, rather than under this prospectus. In addition, the
selling stockholders may transfer the shares of common stock by other means not described in this prospectus. If the selling stockholders effect such transactions by selling shares of common stock to or through underwriters, broker-dealers or
agents, such underwriters, broker-dealers or agents may receive commissions in the form of discounts, concessions or commissions from the selling stockholders or commissions from purchasers of the shares of common stock for whom they may act as
agent or to whom they may sell as principal (which discounts, concessions or commissions as to particular underwriters, broker-dealers or agents may be in excess of those customary in the types of transactions involved). In connection with sales of
the shares of common stock or otherwise, the selling stockholders may enter into hedging transactions with broker-dealers, which may in turn engage in short sales of the shares of common stock in the course of hedging in positions they assume. The
selling stockholders may also sell shares of common stock short and deliver shares of common stock covered by this prospectus to close out short positions and to return borrowed shares in connection with such short sales. The selling stockholders
may also loan or pledge shares of common stock to broker-dealers that in turn may sell such shares. 
 The selling stockholders
may pledge or grant a security interest in some or all of the warrants or shares of common stock owned by them and, if they default in the performance of their secured obligations, the pledgees or secured parties may offer and sell the shares of
common stock from time to time pursuant to this prospectus or any amendment to this prospectus under Rule 424(b)(3) or other applicable provision of the Securities Act amending, if necessary, the list of selling stockholders to include the pledgee,
transferee or other successors in interest as selling stockholders under this prospectus. The selling stockholders also may transfer and donate the shares of common stock in other circumstances in which case the transferees, donees, pledgees or
other successors in interest will be the selling beneficial owners for purposes of this prospectus. 
 To the extent required by
the Securities Act and the rules and regulations thereunder, the selling stockholders and any broker-dealer participating in the distribution of the shares of common stock may be deemed to be “underwriters” within the meaning of the
Securities Act, and any commission paid, or any discounts or concessions allowed to, any such broker-dealer may be deemed to be underwriting commissions or discounts under the Securities Act. At the time a particular offering of the shares of common
stock is made, a prospectus supplement, if required, will be distributed, which will set forth the aggregate amount of shares of common stock being offered and the terms of the offering, including the name or names of any broker-dealers or agents,
any discounts, commissions and other terms constituting compensation from the selling stockholders and any discounts, commissions or concessions allowed or re-allowed or paid to broker-dealers. 

Under the securities laws of some states, the shares of common stock may be sold in such states only through registered or licensed
brokers or dealers. In addition, in some states the 

 
shares of common stock may not be sold unless such shares have been registered or qualified for sale in such state or an exemption from registration or qualification is available and is complied
with. 
 There can be no assurance that any selling stockholder will sell any or all of the shares of common stock registered
pursuant to the registration statement, of which this prospectus forms a part. 
 The selling stockholders and any other person
participating in such distribution will be subject to applicable provisions of the Securities Exchange Act of 1934, as amended, and the rules and regulations thereunder, including, without limitation, to the extent applicable, Regulation M of the
Exchange Act, which may limit the timing of purchases and sales of any of the shares of common stock by the selling stockholders and any other participating person. To the extent applicable, Regulation M may also restrict the ability of any person
engaged in the distribution of the shares of common stock to engage in market-making activities with respect to the shares of common stock. All of the foregoing may affect the marketability of the shares of common stock and the ability of any person
or entity to engage in market-making activities with respect to the shares of common stock. 
 We will pay all expenses of the
registration of the shares of common stock pursuant to the registration rights agreement, estimated to be $[        ] in total, including, without limitation, Securities and Exchange Commission filing fees and
expenses of compliance with state securities or “blue sky” laws; provided, however, a selling stockholder will pay all underwriting discounts and selling commissions, if any. We will indemnify the selling stockholders against liabilities,
including some liabilities under the Securities Act in accordance with the registration rights agreements or the selling stockholders will be entitled to contribution. We may be indemnified by the selling stockholders against civil liabilities,
including liabilities under the Securities Act that may arise from any written information furnished to us by the selling stockholder specifically for use in this prospectus, in accordance with the related registration rights agreements or we may be
entitled to contribution. 
 Once sold under the registration statement, of which this prospectus forms a part, the shares of
common stock will be freely tradable in the hands of persons other than our affiliates.Form of Amendment to the Registration Rights Agreement

 Exhibit 10.3 
 AMENDMENT TO THE REGISTRATION RIGHTS AGREEMENT 
 This
Amendment to that certain Registration Rights Agreement dated October 25, 2012 (the “Registration Rights Agreement”) is made and entered into this 18th day of December, 2012 between ARCA biopharma, Inc., a Delaware corporation (the “Company”), and the other
parties identified on the signature page hereto (the “Buyers”). 
 WITNESSETH 

WHEREAS, in connection with the purchase of common stock in the Company by the Buyers, the parties entered into the
Registration Rights Agreement, pursuant to which the Company agreed to prepare and file a Registration Statement with the SEC not later than the Filing Deadline, and to have the Registration Statement declared effective by the SEC not later than the
Effectiveness Deadline, as those terms are defined in the Registration Rights Agreement; 
 WHEREAS, the
parties agree that it is in their mutual interest to extend the Filing Deadline for an additional 60 days and the Effectiveness Deadline for an additional 90 days; 
 NOW, THEREFORE, in consideration of the premises and the mutual covenants contained herein and for other good and valuable consideration, the receipt
and sufficiency of which are hereby acknowledged, the Company and each of the Buyers hereby agree as follows: 
 I. AMENDMENT

 The Filing Deadline with respect to the filing of the Initial Registration Statement, as defined in
Section 1(e) of the Registration Rights Agreement, shall be extended by an additional 60 calendar days, or 120 calendar days after the Closing Date. The Effectiveness Deadline with respect to the Initial Registration Statement, as defined in
Section 1(d) of the Registration Rights Agreement, shall be extended for an additional 90 calendar days, such that it shall be the earlier of the (A) 180th calendar day after the Closing Date and (B) 4th Business Day after the date the Company is notified (orally or in writing, whichever is earlier) by the SEC that such
Registration Statement will not be reviewed or will not be subject to further review. 
 II. MISCELLANEOUS 

2.1 Except as expressly amended pursuant to this Amendment, all other provisions of the Registration Rights Agreement shall remain
unchanged and in full force and effect. 
 2.2 This Amendment shall be governed by and construed in accordance with the laws of
the State of New York. 

 2.3 Any capitalized terms not defined herein shall have the meanings as set forth in the
Registration Rights Agreement. 
 IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be duly executed
by their respective authorized signatories. 
  

			
	ARCA BIOPHARMA, INC.
		
	By:	 	 /s/ Patrick M. Wheeler

		 	Patrick M. Wheeler, Chief Financial Officer
	
	BUYERS:
	
	Atlas Venture Fund VII, L.P.
		
	By:	 	Atlas Venture
	Its:	 	General Partner
	
	 /s/ Kristen Laguerre

	By:	 	Kristen Laguerre
	Its:	 	Vice President
	
	Investocor Trust
	
	 /s/ Michael R. Bristow

	By:	 	Michael R. Bristow
	Its:	 	Trustee
	
	Lansing Brown Investments, LLC
	
	 /s/ John L. Zabriskie

	By:	 	John L. Zabriskie
	Its:	 	President
	
	Christopher D. Ozeroff
	
	 /s/ Christopher D. Ozeroff

	By:	 	Christopher D. Ozeroff

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