WARRANT TO PURCHASE STOCK

Exhibit 4.3

THIS WARRANT AND THE SHARES ISSUABLE HEREUNDER HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED (THE “ACT”), OR THE SECURITIES LAWS OF ANY STATE AND, EXCEPT AND PURSUANT TO THE PROVISIONS OF ARTICLE 5 BELOW, MAY NOT BE OFFERED, SOLD OR OTHERWISE TRANSFERRED, PLEDGED OR HYPOTHECATED UNLESS AND UNTIL REGISTERED UNDER THE ACT AND APPLICABLE STATE SECURITIES LAW OR, IN THE OPINION OF LEGAL COUNSEL IN FORM AND SUBSTANCE SATISFACTORY TO THE ISSUER OF THESE SECURITIES, SUCH OFFER, SALE OR TRANSFER, PLEDGE OR HYPOTHECATION IS EXEMPT FROM REGISTRATION.

WARRANT TO PURCHASE STOCK

THIS WARRANT CERTIFIES THAT, for the agreed upon value of $1.00 and for other good and valuable consideration, SILICON VALLEY BANK (“Holder”) is entitled to purchase the number of fully paid and nonassessable shares of the class of stock (the “Shares”) of the company (the “Company”) at the Warrant Price all as set forth above and as adjusted pursuant to Article 2 of this Warrant, subject to the provisions and upon the terms and conditions set forth in this Warrant.

ARTICLE 1. EXERCISE.

1.1 Method of Exercise. At any time prior to the Expiration Date, Holder may exercise this Warrant by delivering this Warrant together with a duly executed Notice of Exercise in substantially the form attached as Appendix 1 to the Company at the address set forth in Article 5.6 hereof (or at such other address as the Company may designate from time to time pursuant to Article 5.6 hereof). Unless Holder is exercising the conversion right set forth in Article 1.2, Holder shall also deliver to the Company a check, wire transfer (to an account designated by the Company), or other from of payment acceptable to the Company for the aggregate Warrant Price for the Shares being purchased.

1.2 Conversion Right. In lieu of exercising this Warrant as specified in Article 1.1, Holder may from time to time convert this Warrant, in whole or in part, into a number of Shares determined by dividing (a) the aggregate fair market value of the Shares issuable upon exercise of this Warrant (or, if only a portion of this Warrant is being converted, the aggregate fair market value of the Shares issuable upon exercise of that portion of this Warrant being so converted) minus the aggregate Warrant Price of such Shares by (b) the fair

market value of one Share. The fair market value of the Shares shall be determined pursuant to Article 1.3. In order to exercise its conversion right pursuant to this Article 1.2, Holder shall deliver this Warrant together with a duly executed Notice of Exercise in substantially the form attached as Appendix 1 to the Company at the address set forth in Article 5.6 hereof (or at such other address as the Company may designate from time to time pursuant to Article 5.6 hereof).

1.3 Fair Market Value. If the Company’s common stock is quoted on NASDAQ or listed on any national exchange and the Shares are preferred stock, the fair market value of a Share shall be the closing price of a share of the Company’s common stock as quoted on NASDAQ or listed on such national exchange, as applicable, and reported for the business day immediately before Holder delivers its Notice of Exercise to the Company (or, in the instance where the Warrant is exercised immediately prior to the effectiveness of the Company’s initial public offering, the initial “price to public” per share price specified in the final prospectus relating to such offering), in both cases, multiplied by the number of shares of the Company’s common stock into which a Share is convertible. I f the Company’s common stock is not quoted on NASDAQ or listed on any national exchange, the Board of Directors of the Company shall determine the fair market value in its reasonable good faith judgment.

1.4 Delivery of Certificate and New Warrant. Promptly after Holder exercises or converts this Warrant in accordance with the provisions of this Article 1, and, if applicable, the Company receives payment of the aggregate Warrant Price, the Company shall deliver to Holder certificates for the Shares acquired and, if this Warrant has not been fully exercised or converted and has not expired, a new Warrant representing the Shares not so acquired.

1.5 Replacement of Warrants. On receipt of evidence reasonably satisfactory to the Company of the loss, theft, destruction or mutilation of this Warrant and, in the case of loss, theft or destruction, on delivery of an indemnity agreement reasonably satisfactory in form and amount to the Company or, in the case of mutilation, on surrender and cancellation of this Warrant, the Company shall execute and deliver, in lieu of this Warrant, a new warrant of like tenor.

1.6 Treatment of Warrant Upon Acquisition of Company.

1.6.1 “Acquisition”. For the purpose of this Warrant, “Acquisition” means any sale, license, or other disposition of all or substantially all of the assets of the Company, or any acquisition, reorganization, consolidation, or merger of the Company where the holders of the Company’s securities before the transaction beneficially own less than 50% of the outstanding voting securities of the surviving entity after the transaction.

1.6.2 Treatment of Warrant at Acquisition.

(a) In the event of an Acquisition in which the sole consideration is cash, and, if, on the record date for the Acquisition, the fair market value of the Shares (or other securities issuable upon exercise of this Warrant) is equal to or greater than the Warrant price, Holder agrees that either (a) Holder shall exercise its conversion or purchase right under this Warrant and such exercise will be deemed effective immediately prior to the consummation of such Acquisition or (b) if Holder elects not to exercise the Warrant, this

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Warrant will expire upon the consummation of such Acquisition. The Company shall provide the Holder with written notice of the contemplated Acquisition (together with such information as the Company delivers to stockholders of the Company in connection with such contemplated Acquisition), which is to be delivered to Holder not less than ten (10) days prior to the closing of the proposed Acquisition.

(b) Holder agrees that, in the event of an Acquisition of the Company by an acquirer whose stock is quoted on NASDAQ or listed on any national exchange if, on the record date for the Acquisition, the fair market value of the Shares (or other securities issuable upon exercise of this Warrant) is equal to or greater than the Warrant Price and the consideration to be paid in the Acquisition is either stock of the acquirer or a combination of cash and such stock, the Warrant will be deemed to be automatically exercised pursuant to Article 1.2 hereof, and the Holder shall participate in the Acquisition as a holder of the Shares (or other securities issuable upon exercise of the Warrant) on the same terms as other holders of the same class of securities of the Company.

(c) Upon the closing of any Acquisition other than those particularly described in subsections (a) or (b) above, the successor entity shall assume the obligations of the Warrant, and the Warrant shall be exercisable for the same securities, cash, and property as would be payable for the Shares issuable upon exercise of the unexercised portion of this Warrant as if such Shares were outstanding on the record date for the Acquisition and subsequent closing. The Warrant Price and/or number of Shares shall be adjusted accordingly.

ARTICLE 2. ADJUSTMENTS TO THE SHARES.

2.1 Stock Dividends, Splits, Etc. If the Company declares or pays a dividend on the Shares payable in common stock, or other securities, then upon exercise of this Warrant, for each Share acquired, Holder shall receive, without cost to Holder, the total number and kind of securities to which Holder would have been entitled had Holder owned the Shares of record as of the date the dividend occurred. If the Company subdivides the Shares by reclassification or otherwise into a greater number of shares, the number of Shares purchasable hereunder shall be proportionately increased and the Warrant Price shall be proportionately decreased. If the outstanding shares are combined or consolidated, by reclassification or otherwise, into a lesser number of shares, the Warrant Price shall be proportionately increased and the number of Shares purchasable hereunder shall be proportionately decreased.

2.2 Reclassification, Exchange, Combinations or Substitution. Subject to the provisions of Article 1.6 hereof, upon any reclassification, exchange, substitution, or other event that results in a change of the number and/or class of the securities issuable upon exercise or conversion of this Warrant, Holder shall be entitled to receive, upon exercise or conversion of this Warrant, the number and kind of securities and property that Holder would have received for the Shares if this Warrant had been exercised immediately before such reclassification, exchange, substitution, or other event. Such an event shall include any automatic conversion of the outstanding or issuable securities of the Company of the same class or series as the Shares to common stock pursuant to the terms of the Company’s Certificate of Incorporation upon the closing of a registered public offering of the Company’s common stock. The Company or its successor shall promptly issue to Holder an amendment to this Warrant setting forth the number

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and kind of such new securities or other property issuable upon exercise or conversion of this Warrant as a result of such reclassification, exchange, substitution or other event that results in a change of the number and/or class of securities issuable upon exercise or conversion of this Warrant. The amendment to this Warrant shall provide for adjustments which shall be as nearly equivalent as may be practicable to the adjustments provided for in this Article 2 including, without limitation, adjustments to the Warrant Price and to the number of securities or property issuable upon exercise of the new Warrant. The provisions of this Article 2.2 shall similarly apply to successive reclassifications, exchanges, substitutions, or other events.

2.3 Changes to Antidilution Provisions. Until the earlier to occur of (i) the exercise or conversion in full of this Warrant, or (ii) the Expiration Date, the provisions set forth in Article IV.D.4.(i) of the Company’s Certificate of Incorporation in effect as of the Issue Date may not be amended, modified or waived, without the prior written consent of Holder, unless such amendment, modification or waiver affects the rights associated with the Shares in the same manner as such amendment, modification or waiver affects the rights associated with all other shares of the same series and class as the Shares issuable pursuant to this Warrant.

2.4 Adjustments Based on Loan Availability. If, under the Loan Agreement between Company and Silicon Valley Bank of even date herewith (the “Loan Agreement”), on the Commitment Termination Date (as defined in the Loan Agreement), there is at least $250,000 that has not been Advanced to Company under the Committed Equipment Line, the number of Shares for which this Warrant is exercisable shall be reduced from 26,042 to 17,578 (taking into consideration prior adjustments which may have been made pursuant to Sections 2.1 or 2.2 hereof).

2.5 Fractional Shares. No fractional Shares shall be issuable upon exercise or conversion of the Warrant and the number of Shares to be issued shall be rounded down to the nearest whole Share. If a fractional share interest arises upon any exercise or conversion of the Warrant, the Company shall eliminate such fractional share interest by paying Holder the amount computed by multiplying the fractional interest by the fair market value of a full Share.

2.6 Certificate as to Adjustments. Upon each adjustment of the Warrant Price, the Company shall promptly notify Holder in writing, and, at the Company’s expense, promptly compute such adjustment, and furnish Holder with a certificate of its Chief Financial Officer setting forth such adjustment and the facts upon which such adjustment is based. The Company shall, upon written request, furnish Holder a certificate setting forth the Warrant Price in effect upon the date thereof and the series of adjustments leading to such Warrant Price.

ARTICLE 3. REPRESENTATIONS AND COVENANTS OF THE COMPANY.

3.1 Representations and Warranties. The Company represents and warrants to the Holder as follows:

(a) The initial Warrant Price referenced on the first page of this Warrant is not greater than the price per share at which the Shares were last issued in an arms-length transaction in which at least $500,000 of the Shares were sold.

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(b) All Shares which may be issued upon the exercise of the purchase right represented by this Warrant, and all securities, if any, issuable upon conversion of the Shares, shall, upon issuance, be duly authorized, validly issued, fully paid and nonassessable, and free of any liens and encumbrances except for restrictions on transfer provided for herein or under applicable federal and state securities laws.

(c) The Capitalization Table previously provided to Holder on March     , 2004 remains true and complete as of the Issue Date.

3.2 Notice of Certain Events. If the Company proposes at any time (a) to declare any dividend or distribution upon any of its stock, whether in cash, property, stock, or other securities and whether or not a regular cash dividend; (b) to effect any reclassification or recapitalization of any of its stock; or (c) to merge or consolidate with or into any other corporation, or sell, lease, license, or convey all or substantially all of its assets, or to liquidate, dissolve or wind up, then in connection with each such event, the Company shall give Holder: (1) at least 10 days prior written notice of the date on which a record will be taken for such dividend or distribution (and specifying the date on which the holders of common stock will be entitled thereto) or for determining rights to vote, if any, in respect of the matters referred to in (b) and (c) above; and (2) in the case of the matters referred to in (b) and (c) above at least 10 days prior written notice of the date when the same will take place (and specifying the date on which the holders of common stock will be entitled to exchange their common stock for securities or other property deliverable upon the occurrence of such event).

3.3 Registration Under Securities Act of 1933, as amended. The Company agrees that the Shares issued upon the exercise of this Warrant when so issued, or, if the Shares are convertible into common stock of the Company, such common stock when so issued, shall have the S-3 and “Piggyback,” registration rights pursuant to and as set forth in the Company’s Investor Rights Agreement, dated November 10, 2003, as such may be amended from time to time (the “Investors’ Rights Agreement”).

3.4 No Shareholder Rights. Except as provided in this Warrant, the Holder will not have any rights as a shareholder of the Company until the exercise of this Warrant.

ARTICLE 4. REPRESENTATIONS, WARRANTIES OF THE HOLDER. The Holder represents and warrants to the Company as follows:

4.1 Purchase for Own Account. This Warrant and the securities to be acquired upon exercise of this Warrant by the Holder will be acquired for investment for the Holder’s account, not as a nominee or agent, and not with a view to the public resale or distribution within the meaning of the Act. Holder also represents that the Holder has not been formed for the specific purpose of acquiring this Warrant or the Shares.

4.2 Disclosure of Information. The Holder has received or has had full access to all the information it considers necessary or appropriate to make an informed investment decision with respect to the acquisition of this Warrant and its underlying securities. The Holder further has had an opportunity to ask questions and receive answers from the Company regarding the terms and conditions of the offering of this Warrant and its underlying securities and to

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obtain additional information (to the extent the Company possessed such information or could acquire it without unreasonable effort or expense) necessary to verify any information furnished to the Holder or to which the Holder has access.

4.3 Investment Experience. The Holder understands that the purchase of this Warrant and its underlying securities involves substantial risk. The Holder has experience as an investor in securities of companies in the development stage and acknowledges that the Holder can bear the economic risk of such Holder’s investment in this Warrant and its underlying securities and has such knowledge and experience in financial or business matters that the Holder is capable of evaluating the merits and risks of its investment in this Warrant and its underlying securities and/or has a preexisting personal or business relationship with the Company and certain of its officers, directors or controlling persons of a nature and duration that enables the Holder to be aware of the character, business acumen and financial circumstances of such persons.

4.4 Accredited Investor Status. The Holder is an “accredited investor” within the meaning of Regulation D promulgated under the Act.

4.5 The Act. The Holder understands that this Warrant and the Shares issuable upon exercise or conversion hereof have not been registered un the Act in reliance upon a specific exemption therefrom, which exemption depends upon, among other things, the bona fide nature of the Holder’s investment intent as expressed herein. The Holder understands that this Warrant and the Shares issued upon any exercise or conversion hereof must be held indefinitely unless subsequently registered under the 1933 Act and qualified under applicable state securities laws, or unless exemption from such registration and qualification are otherwise available.

ARTICLE 5. MISCELLANEOUS.

5.1 Term: This Warrant is exercisable in whole or in part at any time and from time to time on or before the Expiration Date.

5.2 Market Stand-Off. Holder agrees to be bound by the “Market Stand-Off” provision (the “Market Stand-Off Agreement”) in Section 2.12 of the Company’s Investors’ Rights Agreement. Until the earlier to occur of (i) the exercise or conversion in full of this Warrant, or (ii) the Expiration Date, the Market Stand-Off Agreement provisions set forth in the Investors’ Rights Agreement may not be amended, modified or waived, without the prior written consent of the Holder, unless such amendment, modification or waiver affects the rights associated with the Shares in the same manner as such amendment, modification or waiver affects the rights associated with all other shares of the same series and class as the Shares issuable pursuant to this Warrant.

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5.3 Legends. The Shares (and the securities issuable, directly or indirectly, upon conversion of the Shares, if any) shall be imprinted with a legend in substantially the following form:

THE SHARES REPRESENTED BY THIS CERTIFICATE HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED (THE “ACT”), OR THE SECURITIES LAWS OF ANY STATE AND MAY NOT BE OFFERED, SOLD OR OTHERWISE TRANSFERRED, PLEDGED OR HYPOTHECATED UNLESS AND UNTIL REGISTERED UNDER THE ACT AND APPLICABLE STATE SECURITIES LAW OR, IN THE OPINION OF LEGAL COUNSEL IN FORM AND SUBSTANCE SATISFACTORY TO THE ISSUER OF THESE SECURITIES, SUCH OFFER, SALE OR TRANSFER, PLEDGE OR HYPOTHECATION IS EXEMPT FROM SUCH REGISTRATION.

5.4 Compliance with Securities Laws on Transfer. This Warrant and the Shares issuable upon exercise of this Warrant (and the securities issuable, directly or indirectly, upon conversion of the Shares, if any) may not be transferred or assigned in whole or in part without compliance with applicable federal and state securities laws by the transferor and the transferee (including, without limitation, the delivery of investment representation letters (and, in the case of a transfer of this Warrant, an executed Assignment substantially in the form of Appendix 3 hereof) and legal opinions reasonably satisfactory to the Company, as reasonably requested by the Company). The Company shall not require Holder to provide an opinion of counsel if the transfer is to Silicon Valley Bancshares (Holder’s parent company) or any other affiliate of Holder. Additionally, the Company shall also not require an opinion of counsel if there is no material question as to the availability of current information as referenced in Rule 144(c), Holder represents that it has complied with Rule 144(d) and (e) in reasonable detail, the selling broker represents that it has complied with Rule 144(f), and the Company is provided with a copy of Holder’s notice of proposed sale.

5.5 Transfer Procedure. Upon receipt by Holder of the executed Warrant, Holder will transfer all of this Warrant to Silicon Valley Bancshares, Holder’s parent company, by execution of an Assignment substantially in the form of Appendix 2. Subject to the provisions of Article 5.4 and upon providing Company with written notice, Silicon Valley Bancshares and any subsequent Holder may transfer all or part of this Warrant or the Shares issuable upon exercise of this Warrant (or the Shares issuable directly or indirectly, upon conversion of the Shares, if any) to any transferee, provided, however, in connection with any such transfer, Silicon Valley Bancshares or any subsequent Holder will give the Company notice of such transfer with the name, address and taxpayer identification number of the transferee and Holder will surrender this Warrant or the certificates representing the Shares issued upon the exercise of this Warrant (or the certificate representing the securities issued on the conversion of such Shares) to the Company for reissuance to the transferee(s) (and Holder if applicable). The Company may refuse to transfer this Warrant or the Shares issued upon the exercise of this Warrant (or the securities issued upon the conversion of such shares) to any person who directly competes with the Company.

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5.6 Notices. All notices and other communications from the Company to the Holder, or vice versa, shall be deemed delivered and effective (i) when given personally or mailed by first-class registered or certified mail, postage prepaid, or (ii) on the first business day after transmission by facsimile, at such address or such facsimile number as may have been furnished to the Company or the Holder, as the case may be, in writing by the Company or such holder from time to time. Effective upon receipt of the fully executed Warrant and the initial transfer described in Article 5.5 above, all notices to the Holder shall be addressed as follows until the Company receives notice of a change of address in connection with a transfer or otherwise:

Silicon Valley Bancshares

Attn: Treasury Department

3003 Tasman Drive, HA 200

Santa Clara, CA 95054

Telephone: 408 ###-###-####

Facsimile: 408 ###-###-####

Notice to the Company shall be addressed as follows until the Holder receives notice of a change in address:

CardioMEMS, Inc.

75 Fifth St., Suite 205

Atlanta, GA 30308

Attn: David Stern, President and CEO

FAX: (404)  ###-###-####

5.7 Waiver. This Warrant and any term hereof may be changed, waived, discharged or terminated only by an instrument in writing signed by the Company and the Holder.

5.8 Attorney’s Fees. In the event of any dispute between the parties concerning the terms and provisions of this Warrant, the party prevailing in such dispute shall be entitled to collect from the other party all costs incurred in such dispute, including reasonable attorney’s fees.

5.9 Automatic Conversion upon Expiration. In the event that, upon the Expiration Date, the fair market value of one Share (or other security issuable upon the exercise hereof) as determined in accordance with Section 1.3 above is greater than the Exercise Price in effect on such date, then this Warrant shall automatically be deemed on and as of such date to be converted pursuant to Section 1.2 above as to all Shares (or such other securities) for which it shall not previously have been exercised or converted, and the Company shall promptly deliver a certificate representing the Shares (or such other securities) issued upon such conversion to the Holder.

5.10 Counterparts. This Warrant may be executed in counterparts, all of which together shall constitute one and the same agreement.

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5.11 Governing Law. This Warrant shall be governed by and construed in accordance with the laws of the State of California, without giving effect to its principles regarding conflicts of law.

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APPENDIX 1

NOTICE OF EXERCISE

1. Holder elects to purchase              shares of the Series B Preferred Stock of CardioMEMS, Inc. pursuant to the terms of the attached Warrant, and tenders payment of the purchase price of the shares in full.

[or]

1. Holder elects to convert the attached Warrant into Shares in the manner specified in the Warrant. This conversion is exercised for              of the Shares covered by the Warrant.

[Strike paragraph that does not apply.]

2. Please issue a certificate or certificates representing the shares in the name specified below:

3. By its execution below and for the benefit of the Company, Holder hereby restates each of the representations and warranties in Article 4 of the Warrant as the date hereof.

APPENDIX 2

ASSIGNMENT

For value received, Silicon Valley Bank hereby sells, assigns and transfers unto

that certain Warrant to Purchase Stock issued by CardioMEMS, Inc. (the “Company”), on                 , 2004 (the “Warrant”) together with all rights, title and interest therein.

By its execution below, and for the benefit of the Company, Silicon Valley Bancshares makes each of the representations and warranties set forth in Article 4 of the Warrant as of the date hereof.

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APPENDIX 3

ASSIGNMENT

For value received,                      hereby sells, assigns and transfers unto

that certain Warrant to Purchase Stock issued by CardioMEMS, Inc. (the “Company”), on                     , 2004 (the “Warrant”) together with all rights, title and interest therein.

By its execution below, and for the benefit of the Company,                      makes each of the representations and warranties set forth in Article 4 of the Warrant as of the date hereof.

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