<PAGE>

                                                                     Exhibit 4.5

THESE SECURITIES HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933 AS
AMENDED, OR ANY STATE SECURITIES LAWS. THEY MAY NOT BE SOLD, OFFERED FOR SALE,
PLEDGED, OR HYPOTHECATED IN THE ABSENCE OF AN EFFECTIVE REGISTRATION STATEMENT
RELATED THERETO OR AN OPINION OF COUNSEL (WHICH MAY BE COMPANY COUNSEL)
REASONABLY SATISFACTORY TO THE COMPANY THAT SUCH REGISTRATION IS NOT REQUIRED
UNDER THE SECURITIES ACT OF 1933, AS AMENDED, OR ANY APPLICABLE STATE SECURITIES
LAWS.

                                WARRANT AGREEMENT

              TO PURCHASE SHARES OF THE SERIES A PREFERRED STOCK OF

                               CYTOKINETICS, INC.

              DATED AS OF SEPTEMBER 25, 1998 (THE "EFFECTIVE DATE")

         WHEREAS, Cytokenetics, Inc., a Delaware corporation (the "Company") has
entered into a Loan And Security Agreement dated as of September 25, 1998, and
related Promissory Note(s) (collectively, the "Loans") with Comdisco, Inc., a
Delaware corporation (the "Warrantholder"); and

         WHEREAS, the Company desires to grant to Warrantholder, in
consideration for such Loans, the right to purchase shares of its Series A
Preferred Stock;

         NOW, THEREFORE, in consideration of the Warrantholder executing and
delivering such Loans and in consideration of mutual covenants and agreements
contained herein, the Company and Warrantholder agree as follows:

1.       GRANT OF THE RIGHT TO PURCHASE PREFERRED STOCK.

         For the first $1,000,000 portion of the Loans, the Company hereby
grants to the Warrantholder, and the Warrantholder is entitled, upon the terms
and subject to the conditions hereinafter set forth, to subscribe to and
purchase, from the Company, 45,000 fully paid and non-assessable shares of the
Company's Series A Preferred Stock ("Preferred Stock") at a purchase price of
$1.00 per share (the "Exercise Price") provided however, that from and after the
effective date of the registration statement for the Company's initial public
offering of its equity securities, the securities purchasable by the
Warrantholder upon the exercise of this Warrant Agreement shall be shares of the
Company's Common Stock ("Common Stock") which shares shall be purchasable by the
Warrantholder in the same number that the Warrantholder would otherwise have
been entitled to purchase had this Warrant Agreement remained exercisable for
shares of the Company's Preferred Stock. From and after the effective date of
the registration statement for the Company's initial public offering of its
equity securities, the Warrantholder shall not have any further right pursuant
to this Warrant Agreement to purchase shares of the Company's Preferred Stock.
The shares of Preferred Stock or Common Stock that are issuable from time to
time upon the exercise of this Warrant Agreement are sometimes referred to
herein as the "Stock.

         In the event that the Company requests and the Warrantholder funds any
portion of the additional $250,000 Advances between the first $1,000,000 and up
to $1,500,000 as provided under the Loans, the Company hereby grants to the
Warrantholder, and the Warrantholder is entitled, upon the terms and subject to
the conditions hereinafter set forth, to subscribe for and purchase, from the
Company, for each Advance funded, 11,250 shares of Stock at the Exercise Price.

         The number and purchase price of such shares are subject to adjustment
as provided in Section 8 hereof.

2.       TERM OF THE WARRANT AGREEMENT.

         Except as otherwise provided for herein, the term of this Warrant
Agreement and the right to purchase Stock as granted herein shall commence on
the Effective Date and shall be exercisable for a period of (i) seven (7) years
or (ii) three (3) years from the effective date of the Company's initial public
offering, whichever is shorter.

                                     - 1 -
<PAGE>

3.       EXERCISE OF THE PURCHASE RIGHTS.

         The purchase rights set forth in this Warrant Agreement are exercisable
by the Warrantholder, in whole or in part, at any time, or from time to time,
prior to the expiration of the term set forth in Section 2 above, by tendering
to the Company at its principal office a notice of exercise in the form attached
hereto as Exhibit I (the "Notice of Exercise"), duly completed and executed.
Promptly upon receipt of the Notice of Exercise and the payment of the purchase
price in accordance with the terms set forth below, and in no event later than
twenty-one (21) days thereafter, the Company shall issue to the Warrantholder a
certificate for the number of shares of Stock purchased and shall execute the
acknowledgment of exercise in the form attached hereto as Exhibit II (the
"Acknowledgment of Exercise") indicating the number of shares which remain
subject to future purchases, if any.

         The Exercise Price may be paid at the Warrantholder's election either
(i) by cash or check, or (ii) by surrender of Warrants ("Net Issuance") as
determined below. If the Warrantholder elects the Net Issuance method, the
Company will issue Stock in accordance with the following formula:

                    X = Y(A-B)
                        ------
                          A

         Where: X = the number of shares of Stock to be issued to the
Warrantholder.

                     Y = the number of shares of Stock requested to be exercised
                         under this Warrant Agreement.

                     A = the fair market value of one (1) share of Stock.

                     B = the Exercise Price.

         For purposes of the above calculation, current fair market value of
Stock shall mean with respect to each share of Stock:

                  (i)      if the exercise is in connection with an initial
         public offering of the Company's Common Stock, and if the Company's
         Registration Statement relating to such public offering has been
         declared effective by the SEC, then the fair market value per share
         shall be the product of (x) the initial "Price to Public" specified in
         the final prospectus with respect to the offering and (y) the number of
         shares of Common Stock into which each share of Stock is convertible at
         the time of such exercise;

                  (ii)     if this Warrant is exercised after, and not in
         connection with the Company's initial public offering, and:

                           (a)      if traded on a securities exchange, the fair
                  market value shall be deemed to be the product of (x) the
                  average of the closing prices over a twenty-one (21) day
                  period ending three days before the day the current fair
                  market value of the securities is being determined and (y) the
                  number of shares of Common Stock into which each share of
                  Stock is convertible at the time of such exercise; or

                           (b)      if actively traded over-the-counter, the
                  fair market value shall be deemed to be the product of (x) the
                  average of the closing bid and asked prices quoted on the
                  NASDAQ system (or similar system) over the twenty-one (21) day
                  period ending three days before the day the current fair
                  market value of the securities is being determined and (y) the
                  number of shares of Common Stock into which each share of
                  Stock is convertible at the time of such exercise;

                  (iii)    if at any time the Common Stock is not listed on any
         securities exchange or quoted in the NASDAQ System or the
         over-the-counter market, the current fair market value of Stock shall
         be the product of (x) the highest price per share which the Company
         could obtain from a willing buyer (not a current employee or director)
         for shares of Common Stock sold by the Company, from authorized but
         unissued shares, as determined in good faith by its Board of Directors
         and (y) the number of shares of Common Stock into which each shares of
         Stock is convertible at the time of such exercise unless the Company
         shall become subject to a merger, acquisition or other consolidation
         pursuant to which the Company is not the surviving party, in which case
         the fair market value of Stock shall be deemed to be the value received
         by the holders of the Company's Stock on a common equivalent basis
         pursuant to such merger or acquisition.

                                     - 2 -

<PAGE>

         Upon partial exercise by either cash or Net Issuance, the Company shall
promptly issue an amended Warrant Agreement representing the remaining number of
shares purchasable hereunder. All other terms and conditions of such amended
Warrant Agreement shall be identical to those contained herein, including, but
not limited to the Effective Date hereof.

4.       RESERVATION OF SHARES.

         (a)      Authorization and Reservation of Shares. During the term of
this Warrant Agreement, the Company will at all times have authorized and
reserved a sufficient number of shares of its Stock to provide for the exercise
of the rights to purchase Stock as provided for herein.

         (b)      Registration or Listing. If any shares of Stock required to be
reserved hereunder require registration with or approval of any governmental
authority under any Federal or State law (other than any registration under the
Securities Act of 1933, as amended ("1933 Act"), as then in effect, or any
similar Federal statute then enforced, or any state securities law, required by
reason of any transfer involved in such conversion), or listing on any domestic
securities exchange, before such shares may be issued upon conversion, the
Company will, at its expense and as expeditiously as possible, use its best
efforts to cause such shares to be duly registered, listed or approved for
listing on such domestic securities exchange, as the case may be.

5.       NO FRACTIONAL SHARES OR SCRIP.

         No fractional shares or scrip representing fractional shares shall be
issued upon the exercise of the Warrant, but in lieu of such fractional shares
the Company shall make a cash payment therefor upon the basis of the Exercise
Price then in effect.

6.       NO RIGHTS AS SHAREHOLDER.

         This Warrant Agreement does not entitle the Warrantholder to any voting
rights or other rights as a shareholder of the Company prior to the exercise of
the Warrant.

7.       WARRANTHOLDER REGISTRY.

         The Company shall maintain a registry showing the name and address of
the registered holder of this Warrant Agreement.

8.       ADJUSTMENT RIGHTS.

         The purchase price per share and the number of shares of Stock
purchasable hereunder are subject to adjustment, as follows:

         (a)      Merger and Sale of Assets. If at any time there shall be a
capital reorganization of the shares of the Company's stock (other than a
combination, reclassification, exchange or subdivision of shares otherwise
provided for herein), or a merger or consolidation of the Company with or into
another corporation whether or not the Company is the surviving corporation, or
the sale of all or substantially all of the Company's properties and assets to
any other person (hereinafter referred to as a "Merger Event"), then, as a part
of such Merger Event, lawful provision shall be made so that the Warrantholder
shall thereafter be entitled to receive, upon exercise of the Warrant, the
number of shares of preferred stock or other securities of the successor
corporation resulting from such Merger Event, equivalent in value to that which
would have been issuable if Warrantholder had exercised this Warrant immediately
prior to the Merger Event. In any such case, appropriate adjustment (as
determined in good faith by the Company's Board of Directors) shall be made in
the application of the provisions of this Warrant Agreement with respect to the
rights and interest of the Warrantholder after the Merger Event to the end that
the provisions of this Warrant Agreement (including adjustments of the Exercise
Price and number of shares of Preferred Stock purchasable) shall be applicable
to the greatest extent possible.

         (b)      Reclassification of Shares. If the Company at any time shall,
by combination, reclassification, exchange or subdivision of securities or
otherwise, change any of the securities as to which purchase rights under this
Warrant Agreement exist into the same or a different number of securities of any
other class or classes, this Warrant Agreement shall thereafter represent the
right to acquire such number and kind of securities as would have been issuable
as the result of such change with respect to the securities which were subject
to the purchase rights

                                     - 3 -

<PAGE>

under this Warrant Agreement immediately prior to such combination,
reclassification, exchange, subdivision or other change.

         (c)      Subdivision or Combination of Shares. If the Company at any
time shall combine or subdivide its Stock, the Exercise Price shall be
proportionately decreased in the case of a subdivision, or proportionately
increased in the case of a combination.

         (d)      Stock Dividends. If the Company at any time shall pay a
dividend payable in, or make any other distribution (except any distribution
specifically provided for in the foregoing subsections (a) or (b)) of the
Company's stock, then the Exercise Price shall be adjusted, from and after the
record date of such dividend or distribution, to that price determined by
multiplying the Exercise Price in effect immediately prior to such record date
by a fraction (i) the numerator of which shall be the total number of all shares
of the Company's stock outstanding immediately prior to such dividend or
distribution, and (ii) the denominator of which shall be the total number of all
shares of the Company's stock outstanding immediately after such dividend or
distribution. The Warrantholder shall thereafter be entitled to purchase, at the
Exercise Price resulting from such adjustment, the number of shares of Stock
(calculated to the nearest whole share) obtained by multiplying the Exercise
Price in effect immediately prior to such adjustment by the number of shares of
Stock issuable upon the exercise hereof immediately prior to such adjustment and
dividing the product thereof by the Exercise Price resulting from such
adjustment.

         (e)      Antidilution Rights. Additional antidilution rights applicable
to the Preferred Stock purchasable hereunder are as set forth in the Company's
Certificate of Incorporation, as amended through the Effective Date, a true and
complete copy of which is attached hereto as Exhibit _ (the "Charter"). The
Company shall promptly provide the Warrantholder with any restatement,
amendment, modification or waiver of the Charter. The Company shall provide
Warrantholder with prior written notice of any issuance of its stock or other
equity security to occur after the Effective Date of this Warrant, which notice
shall include (a) the price at which such stock or security is to be sold, (b)
the number of shares to be issued, and (c) such other information as necessary
for Warrantholder to determine if a dilutive event has occurred.

         (f)      Notice of Adjustments. If: (i) the Company shall declare any
dividend or distribution upon its stock, whether in cash, property, stock or
other securities; (ii) the Company shall offer for subscription prorata to the
holders of any class of its Preferred or other convertible stock any additional
shares of stock of any class or other rights; (iii) there shall be any Merger
Event; (iv) there shall be an initial public offering; or (v) there shall be any
voluntary dissolution, liquidation or winding up of the Company; then, in
connection with each such event, the Company shall send to the Warrantholder:
(A) at least twenty (20) days' prior written notice of the date on which the
books of the Company shall close or a record shall be taken for such dividend,
distribution, subscription rights (specifying the date on which the holders of
Stock shall be entitled thereto) or for determining rights to vote in respect of
such Merger Event, dissolution, liquidation or winding up; (B) in the case of
any such Merger Event, dissolution, liquidation or winding up, at least twenty
(20) days' prior written notice of the date when the same shall take place (and
specifying the date on which the holders of Stock shall be entitled to exchange
their Stock for securities or other property deliverable upon such Merger Event,
dissolution, liquidation or winding up); and (C) in the case of a public
offering, the Company shall give the Warrantholder at least twenty (20) days
written notice prior to the effective date thereof.

         Each such written notice shall set forth, in reasonable detail, (i) the
event requiring the adjustment, (ii) the amount of the adjustment, (iii) the
method by which such adjustment was calculated, (iv) the Exercise Price, and (v)
the number of shares subject to purchase hereunder after giving effect to such
adjustment, and shall be given by first class mail, postage prepaid, addressed
to the Warrantholder, at the address as shown on the books of the Company.

         (g)      Timely Notice. Failure to timely provide such notice required
by subsection (f) above shall entitle Warrantholder to retain the benefit of the
applicable notice period notwithstanding anything to the contrary contained in
any insufficient notice received by Warrantholder. The notice period shall begin
on the date Warrantholder actually receives a written notice containing all the
information specified above.

9.       REPRESENTATIONS, WARRANTIES AND COVENANTS OF THE COMPANY.

         (a)      Reservation of Stock. The Stock issuable upon exercise of the
Warrantholder's rights has been duly and validly reserved and, when issued in
accordance with the provisions of this Warrant Agreement, will be validly
issued, fully paid and non-assessable, and will be free of any taxes, liens,
charges or encumbrances of any nature whatsoever; provided, however, that the
Stock issuable pursuant to this Warrant Agreement may be subject

                                     - 4 -

<PAGE>

to restrictions on transfer under state and/or Federal securities laws. The
Company has made available to the Warrantholder true, correct and complete
copies of its Charter and Bylaws, as amended. The issuance of certificates for
shares of Stock upon exercise of the Warrant Agreement shall be made without
charge to the Warrantholder for any issuance tax in respect thereof, or other
cost incurred by the Company in connection with such exercise and the related
issuance of shares of Stock. The Company shall not be required to pay any tax
which may be payable in respect of any transfer involved and the issuance and
delivery of any certificate in a name other than that of the Warrantholder.

         (b)      Due Authority. The execution and delivery by the Company of
this Warrant Agreement and the performance of all obligations of the Company
hereunder, including the issuance to Warrantholder of the right to acquire the
shares of Stock, have been duly authorized by all necessary corporate action on
the part of the Company, and the Loans and this Warrant Agreement are not
inconsistent with the Company's Charter or Bylaws, do not contravene any law or
governmental rule, regulation or order applicable to it, do not and will not
contravene any provision of, or constitute a default under, any indenture,
mortgage, contract or other instrument to which it is a party or by which it is
bound, and the Loans and this Warrant Agreement constitute legal, valid and
binding agreements of the Company, enforceable in accordance with their
respective terms.

         (c)      Consents and Approvals. No consent or approval of, giving of
notice to, registration with, or taking of any other action in respect of any
state, Federal or other governmental authority or agency is required with
respect to the execution, delivery and performance by the Company of its
obligations under this Warrant Agreement, except for the filing of notices
pursuant to Regulation D under the 1933 Act and any filing required by
applicable state securities law, which filings will be effective by the time
required thereby.

         (d)      Issued Securities. All issued and outstanding shares of Common
Stock, Preferred Stock or any other securities of the Company have been duly
authorized and validly issued and are fully paid and nonassessable. All
outstanding shares of Common Stock, Preferred Stock and any other securities
were issued in full compliance with all Federal and state securities laws. In
addition:

                  (i)      The authorized capital of the Company consists of (A)
         10,000,000 shares of Common Stock, of which 1,126,110 shares are issued
         and outstanding, and (B) 5,550,000 shares of preferred stock, of which
         5,300,000 shares are issued and outstanding and are convertible into
         5,550,000 shares of Common Stock at $1.00 per share.

                  (ii)     The Company has reserved (A) 2,000,000 shares of
         Common Stock for issuance under its under its 1997 Stock Option/Stock
         Issuance Plan under which 1,503,890 options have been granted. There
         are no other options, warrants, conversion privileges or other rights
         presently outstanding to purchase or otherwise acquire any authorized
         but unissued shares of the Company's capital stock or other securities
         of the Company.

                  (iii)    In accordance with the Company's Articles of
         Incorporation, no shareholder of the Company has preemptive rights to
         purchase new issuances of the Company's capital stock.

         (e)      Insurance. The Company has in full force and effect insurance
policies, with extended coverage, insuring the Company and its property and
business against such losses and risks, and in such amounts, as are customary
for corporations engaged in a similar business and similarly situated and as
otherwise may be required pursuant to the terms of any other contract or
agreement.

         (f)      Exempt Transaction. Subject to the accuracy of the
Warrantholder's representations in Section 10 hereof, the issuance of the Stock
upon exercise of this Warrant will constitute a transaction exempt from (i) the
registration requirements of Section 5 of the 1933 Act, in reliance upon Section
4(2) thereof, and (ii) the qualification requirements of the applicable state
securities laws.

         (g)      Compliance with Rule 144. At the written request of the
Warrantholder, who proposes to sell Stock issuable upon the exercise of the
Warrant in compliance with Rule 144 promulgated by the Securities and Exchange
Commission, the Company shall furnish to the Warrantholder, within ten days
after receipt of such request, a written statement confirming the Company's
compliance with the filing requirements of the Securities and Exchange
Commission as set forth in such Rule, as such Rule may be amended from time to
time.

10.      REPRESENTATIONS AND COVENANTS OF THE WARRANTHOLDER.

                                     - 5 -

<PAGE>

         This Warrant Agreement has been entered into by the Company in reliance
upon the following representations and covenants of the Warrantholder:

         (a)      Investment Purpose. The right to acquire Stock issuable upon
exercise of the Warrantholder's rights contained herein will be acquired for
investment and not with a view to the sale or distribution of any part thereof,
and the Warrantholder has no present intention of selling or engaging in any
public distribution of the same except pursuant to a registration or exemption.

         (b)      Private Issue. The Warrantholder understands (i) that the
Stock issuable upon exercise of this Warrant is not registered under the 1933
Act or qualified under applicable state securities laws on the ground that the
issuance contemplated by this Warrant Agreement will be exempt from the
registration and qualifications requirements thereof, and (ii) that the
Company's reliance on such exemption is predicated on the representations set
forth in this Section 10.

         (c)      Disposition of Warrantholder's Rights. In no event will the
Warrantholder make a disposition of any of its rights to acquire Stock issuable
upon exercise of such rights unless and until (i) it shall have notified the
Company of the proposed disposition, and (ii) if requested by the Company, it
shall have furnished the Company with an opinion of counsel (which counsel may
either be inside or outside counsel to the Warrantholder) satisfactory to the
Company and its counsel to the effect that (A) appropriate action necessary for
compliance with the 1933 Act has been taken, or (B) an exemption from the
registration requirements of the 1933 Act is available. Notwithstanding the
foregoing, the restrictions imposed upon the transferability of any of its
rights to acquire Stock issuable on the exercise of such rights do not apply to
transfers from the beneficial owner of any of the aforementioned securities to
its nominee or from such nominee to its beneficial owner, and shall terminate as
to any particular share of Stock when (1) such security shall have been
effectively registered under the 1933 Act and sold by the holder thereof in
accordance with such registration or (2) such security shall have been sold
without registration in compliance with Rule 144 under the 1933 Act, or (3) a
letter shall have been issued to the Warrantholder at its request by the staff
of the Securities and Exchange Commission or a ruling shall have been issued to
the Warrantholder at its request by such Commission stating that no action shall
be recommended by such staff or taken by such Commission, as the case may be, if
such security is transferred without registration under the 1933 Act in
accordance with the conditions set forth in such letter or ruling and such
letter or ruling specifies that no subsequent restrictions on transfer are
required. Whenever the restrictions imposed hereunder shall terminate, as
hereinabove provided, the Warrantholder or holder of a share of Stock then
outstanding as to which such restrictions have terminated shall be entitled to
receive from the Company, without expense to such holder, one or more new
certificates for the Warrant or for such shares of Stock not bearing any
restrictive legend.

         (d)      Financial Risk. The Warrantholder has such knowledge and
experience in financial and business matters as to be capable of evaluating the
merits and risks of its investment, and has the ability to bear the economic
risks of its investment.

         (e)      Risk of No Registration. The Warrantholder understands that if
the Company does not register with the Securities and Exchange Commission
pursuant to Section 12 of the 1934 Act (the "1934 Act"), or file reports
pursuant to Section 15(d), of the 1934 Act", or if a registration statement
covering the securities under the 1933 Act is not in effect when it desires to
sell (i) the rights to purchase Stock pursuant to this Warrant Agreement, or
(ii) the Stock issuable upon exercise of the right to purchase, it may be
required to hold such securities for an indefinite period. The Warrantholder
also understands that any sale of its rights of the Warrantholder to purchase
Stock which might be made by it in reliance upon Rule 144 under the 1933 Act
may be made only in accordance with the terms and conditions of that Rule.

         (f)      Accredited Investor. Warrantholder is an "accredited investor"
within the meaning of the Securities and Exchange Rule 501 of Regulation D, as
presently in effect.

11.      TRANSFERS.

         Subject to the terms and conditions contained in Section 10 hereof,
this Warrant Agreement and all rights hereunder are transferable in whole or in
part by the Warrantholder and any successor transferee, provided, however, in no
event shall the number of transfers of the rights and interests in all of the
Warrants exceed three (3) transfers. The transfer shall be recorded on the books
of the Company upon receipt by the Company of a notice of

                                     - 6 -

<PAGE>

transfer in the form attached hereto as Exhibit III (the "Transfer Notice"), at
its principal offices and the payment to the Company of all transfer taxes and
other governmental charges imposed on such transfer.

12.      MISCELLANEOUS.

         (a)      Effective Date. The provisions of this Warrant Agreement shall
be construed and shall be given effect in all respects as if it had been
executed and delivered by the Company on the date hereof. This Warrant Agreement
shall be binding upon any successors or assigns of the Company.

         (b)      Attorney's Fees. In any litigation, arbitration or court
proceeding between the Company and the Warrantholder relating hereto, the
prevailing party shall be entitled to attorneys' fees and expenses and all costs
of proceedings incurred in enforcing this Warrant Agreement.

         (c)      Governing Law. This Warrant Agreement shall be governed by and
construed for all purposes under and in accordance with the laws of the State of
Illinois.

         (d)      Counterparts. This Warrant Agreement may be executed in two or
more counterparts, each of which shall be deemed an original, but all of which
together shall constitute one and the same instrument.

         (e)      Notices. Any notice required or permitted hereunder shall be
given in writing and shall be deemed effectively given upon personal delivery,
facsimile transmission (provided that the original is sent by personal delivery
or mail as hereinafter set forth) or seven (7) days after deposit in the United
States mail, by registered or certified mail, addressed (i) to the Warrantholder
at 6111 North River Road, Rosemont, Illinois 60018, attention: Venture Lease
Administration, cc: Legal Department, attn.: General Counsel, (and/or, if by
facsimile, (847) 518-5465 and (847)518-5088 and (ii) to the Company at 280 East
Grand Avenue, Suite 2, South San Francisco, CA 94080, attention: President
(and/or if by facsimile, (650) 624-3010 or at such other address as any such
party may subsequently designate by written notice to the other party.

         (f)      Remedies. In the event of any default hereunder, the
non-defaulting party may proceed to protect and enforce its rights either by
suit in equity and/or by action at law, including but not limited to an action
for damages as a result of any such default, and/or an action for specific
performance for any default where Warrantholder will not have an adequate remedy
at law and where damages will not be readily ascertainable. The Company
expressly agrees that it shall not oppose an application by the Warrantholder or
any other person entitled to the benefit of this Agreement requiring specific
performance of any or all provisions hereof or enjoining the Company from
continuing to commit any such breach of this Agreement.

         (g)      No Impairment of Rights. The Company will not, by amendment of
its Charter or through any other means, avoid or seek to avoid the observance or
performance of any of the terms of this Warrant, but will at all times in good
faith assist in the carrying out of all such terms and in the taking of all such
actions as may be necessary or appropriate in order to protect the rights of the
Warrantholder against impairment.

         (h)      Survival. The representations, warranties, covenants and
conditions of the respective parties contained herein or made pursuant to this
Warrant Agreement shall survive the execution and delivery of this Warrant
Agreement.

         (i)      Severability. In the event any one or more of the provisions
of this Warrant Agreement shall for any reason be held invalid, illegal or
unenforceable, the remaining provisions of this Warrant Agreement shall be
unimpaired, and the invalid, illegal or unenforceable provision shall be
replaced by a mutually acceptable valid, legal and enforceable provision, which
comes closest to the intention of the parties underlying the invalid, illegal or
unenforceable provision.

         (j)      Amendments. Any provision of this Warrant Agreement may be
amended by a written instrument signed by the Company and by the Warrantholder.

                                     - 7 -

<PAGE>

         IN WITNESS WHEREOF, the parties hereto have caused this Warrant
Agreement to be executed by its officers thereunto duly authorized as of the
Effective Date.

                                    COMPANY: CYTOKENETICS, INC.

                                    By: /s/ JON C. RICHARDS
                                        ---------------------
                                    Title: Chief Financial Officer

                                    WARRANTHOLDER: COMDISCO, INC.

                                    By: /s/ JAMES P. LABE
                                        ---------------------
                                    Title: JAMES P. LABE
                                           PRESIDENT COMDISCO VENTURES DIVISION

                                     - 8 -

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                                    EXHIBIT I

                               NOTICE OF EXERCISE

TO:      ________________________

(1)      The undersigned Warrantholder hereby elects to purchase _________
         shares of the Series A Preferred Stock of ___________, pursuant to the
         terms of the Warrant Agreement dated the ____ day of _________ 19___
         (the "Warrant Agreement") between _____________________ and the
         Warrantholder, and tenders herewith payment of the purchase price for
         such shares in full, together with all applicable transfer taxes, if
         any.

(2)      In exercising its rights to purchase the Series A Preferred Stock of
         ________________, the undersigned hereby confirms and acknowledges the
         investment representations and warranties made in Section 10 of the
         Warrant Agreement.

(3)      Please issue a certificate or certificates representing said shares of
         Series A Preferred Stock in the name of the undersigned or in such
         other name as is specified below.

_______________________________
(Name)

_______________________________
(Address)

WARRANTHOLDER: COMDISCO, INC.

By:    _________________________

Title: _________________________

Date:  _________________________

                                     - 9 -

<PAGE>

                                   EXHIBIT II

                           ACKNOWLEDGMENT OF EXERCISE

         The undersigned _________________ , hereby acknowledge receipt of the
"Notice of Exercise" from Comdisco, Inc., to purchase _______ shares of the
Series A Preferred Stock of____________ pursuant to the terms of the Warrant
Agreement, and further acknowledges that _______ shares remain
subject to  purchase under the terms of the Warrant Agreement,

                                 COMPANY:

                                 By:    _______________________

                                 Title: _______________________

                                 Date:  _______________________

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<PAGE>

                                  EXHIBIT III

                                TRANSFER NOTICE

(TO TRANSFER OR ASSIGN THE FOREGOING WARRANT AGREEMENT EXECUTE THIS FORM AND
SUPPLY REQUIRED INFORMATION. DO NOT USE THIS FORM TO PURCHASE SHARES.)

         FOR VALUE RECEIVED, the foregoing Warrant Agreement and all rights
evidenced thereby are hereby transferred and assigned to

___________________________________________________________
(Please Print)

whose address is
___________________________________________________________

___________________________________________________________

                      Dated: ______________________________

                      Holder's Signature: _________________

                      Holder's Address: ___________________

                      _____________________________________

Signature Guaranteed: _____________________________________

NOTE:    The signature to this Transfer Notice must correspond with the name as
         it appears on the face of the Warrant Agreement, without alteration or
         enlargement or any change whatever. Officers of corporations and those
         acting in a fiduciary or other representative capacity should file
         proper evidence of authority to assign the foregoing Warrant Agreement.

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