Document:

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                                                                     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.

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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.

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         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

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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

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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.

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         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

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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.

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         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

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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:  _________________________

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                                   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:  _______________________

                                     - 10 -

<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.

                                     - 11 -<PAGE>

                                                                     Exhibit 4.6

                          LOAN AND SECURITY AGREEMENT

         THIS AGREEMENT (the "Agreement"), dated as of December 16, 1999 (the
"Closing Date") is entered into by and between Cytokinetics, Incorporated, a
Delaware corporation having a principal place of business at 280 East Grand
Avenue, South San Francisco, CA 94080 (the "Borrower") and Comdisco, Inc., a
Delaware corporation having a principal place of business at 6111 North River
Road, Rosemont, Illinois 60018 (the "Lender"). In consideration of the mutual
agreements contained herein, the parties hereto agree as follows:

         WHEREAS, Borrower has requested Lender to make available to Borrower a
loan in the aggregate principal amount of up to FIVE MILLION and 00/100 DOLLARS
($5,000,000) (as the same may from time to time be amended, modified,
supplemented or revised, the "Loan"), which shall be available in minimum
installments of TWO HUNDRED FIFTY THOUSAND and 00/100 DOLLARS ($250,000) each
(the "Advance") on various dates prior to December 16, 2000 ("Advance Date(s)"),
which would be evidenced by Secured Promissory Note(s) executed by Borrower
substantially in the form of EXHIBIT A-1 AND A-2 hereto (as the same may from
time to time be amended, modified, supplemented or restated the "Note(s)");

         NOW, THEREFORE, it is agreed:

SECTION 1. THE LOAN

         1.1      Subject to the terms and conditions set forth herein, Lender
shall lend to Borrower the aggregate original principal amount of FIVE MILLION
AND 00/100 DOLLARS ($5,000,000) in two parts, the first part in the amount of
Two Million Dollars ($2,000,000) ("Part I") and the second part in the amount of
Three Million dollars ($3,000,000) ("Part II') together with interest at the
rate of eight and one quarter percent (8.25%) per annum due and payable in
monthly installments as set forth in the Note.

         Proceeds of this Loan may finance computers, workstations, peripherals,
instrumentation, electronic test equipment, office furniture, certain microscopy
equipment and other equipment approved by Lender and evidenced by Secured
Promissory Note(s) executed by Borrower substantially in the form of EXHIBIT A-1
.. Up to 20% of the Loan may be used to finance software and tenant improvements
evidenced by Secured Promissory Note(s) executed by Borrower substantially in
the form of EXHIBIT A-2. Lender will not finance custom equipment, installation
costs, delivery costs, rolling stock, special tooling, molds and hand held
items.

         1.2      Upon the occurrence of and during an Event of Default (as
defined herein), interest shall thereafter be calculated at a rate of five
percent (5%) in excess of the rate that would otherwise be applicable ("Default
Rate"). All such interest shall be due and payable in arrears, on the first day
of the following month.

         1.3      Notwithstanding any provision in this Agreement, the Note, or
any other "Loan Document" (as defined herein), it is not the parties' intent to
contract for, charge or receive interest at a rate that is greater than the
maximum rate permissible by law which a court of competent jurisdiction shall
deem applicable hereto (which under the laws of the State of Illinois shall be
deemed to be the laws relating to permissible rates of interest on commercial
loans) (the "Maximum Rate"). If the Borrower actually pays Lender an amount of
interest, chargeable on the

Loan and Security Agr.                 -1-

<PAGE>

total aggregate principal Secured Obligations of Borrower under this Agreement
and the Note (as said rate is calculated over a period of time that is the
longer of (i) the time from the date of this Agreement through the maturity time
as set forth on the Note, or (ii) the entire period of time that any principal
is outstanding on the Note), which amount of interest exceeds interest
calculated at the Maximum Rate on said principal chargeable over said period of
time, then such excess interest actually paid by Borrower shall be applied
first, to the payment of principal outstanding on the Note; second, after all
principal is repaid, to the payment of Lender's out of pocket costs, expenses,
and professional fees which are owed by Borrower to Lender under this Agreement
or the Loan Documents; and third, after all principal, costs, expenses, and
professional fees owed by Borrower to Lender are repaid, the excess (if any)
shall be refunded to Borrower.

         1.4      In the event any interest is not paid when due hereunder,
delinquent interest shall be added to principal and shall bear interest on
interest, compounded at the rate set forth in Section 1.1.

         1.5      Upon and during the continuation of an Event of Default
hereunder (as defined herein), all Secured Obligations, including principal,
interest, compounded interest, and reasonable professional fees, shall bear
interest at a rate per annum equal to the Default Rate.

         1.6      Borrower shall have the option to prepay the Note, in whole or
in part, at any time after the date hereof by paying the principal amount
together with all accrued and unpaid interest with respect to such principal
amount, as of the date of such prepayment and the Balloon Payment as described
in the Note together with a prepayment premium equal to the difference, if any,
between (x) the amount being prepaid and (y) the present value, discounted at
the Treasury Rate, of each installment of principal and interest being prepaid
discounted to the date of prepayment. If the amount in (x) is greater than the
amount in (y), no prepayment premium shall be due. The "Treasury Rate" shall
mean the then prevailing yield on US Treasury Constant Maturities for the most
recent business day, as quoted in the Federal Reserve Statistical Release H15,
as of the date of prepayment for an obligation of comparable maturity to the
maturity date of the Note.

SECTION 2. SECURITY INTEREST

         As security for the payment of all indebtedness ("Indebtedness") of the
Borrower to the Lender hereunder and under the Note, as the same may be renewed,
extended for any period or rearranged, and the performance by the Borrower of
its other obligations hereunder (the Indebtedness and such other obligations
being hereinafter sometimes collectively referred to as the "Secured
Obligations"), the Borrower hereby assigns to the Lender, and grants to the
Lender a first priority security interest in, all the Borrower's right, title,
and interest in and to the following property ("Collateral"): (i) the equipment
and other property (the "Equipment") described in Exhibit B attached hereto; and
(ii) all proceeds, products, replacements, additions to, substitutions for and
accessions to any and all Equipment including, without limitation, the proceeds
applicable to the insurance referred to in Section 4 hereof.

         Equipment shall consist of computers, workstations, peripherals,
instrumentation, electronic test equipment, office furniture, certain types of
microscopy equipment and other items of equipment approved by Lender. Up to 20%
of the Loan may be used for software and tenant improvements.

Loan and Security Agr.                 -2-

<PAGE>

SECTION 3. REPRESENTATIONS AND WARRANTIES OF BORROWER

The Borrower represents, warrants and agrees that:

         3.1      it has good title in and to the Equipment, free of all liens,
security interests, encumbrances and claims whatsoever, except for the interest
of the Lender therein;

         3.2      it has the full power and authority to, and does hereby grant
and convey to the Lender, a valid first priority perfected security interest in
the Collateral as security for the Secured Obligations, free of all liens,
security interests, encumbrances and claims, and shall execute such Uniform
Commercial Code ("UCC") financing statements in connection herewith as the
Lender may reasonably request. No other lien, security interest, adverse claim
or encumbrance has been created by Borrower or is known by Borrower to exist
with respect to any Collateral;

         3.3      it is a corporation duly organized, legally existing and in
good standing under the laws of the State of Delaware, and is duly qualified as
a foreign corporation in all jurisdictions where the failure to so qualify would
have a material adverse effect on the Collateral or the business of the Borrower
taken as a whole;

         3.4      the execution, delivery and performance of the Note, this
Agreement, the Warrant Agreement dated December 16, 1999 pursuant to which
Borrower granted to Lender the right to purchase the number of shares of
preferred stock as set forth therein ("Warrant Agreement"), and all financing
statements, certificates and other documents required to be delivered or
executed in connection herewith (collectively, the "Loan Documents") have been
duly authorized by all necessary corporate action of Borrower, the individual or
individuals executing the Loan Documents were duly authorized to do so, the
Equipment is personal property and as used by the Borrower will not be or become
fixtures under applicable law, and the Loan Documents constitute legal, valid
and binding obligations of the Borrower, enforceable in accordance with their
respective terms, subject to applicable bankruptcy, insolvency, reorganization
or other similar laws generally affecting the enforcement of the rights of
creditors;

         3.5      the Loan Documents do not and will not violate any provisions
of its Certificate of Incorporation, bylaws or any contract, agreement, law,
regulation, order, injunction, judgment, decree or writ to which the Borrower is
subject, or result in the creation or imposition of any lien, security interest
or other encumbrance upon the Collateral, other than those created by this
Agreement;

         3.6      the execution, delivery and performance of the Loan Documents
do not require the consent or approval of any other person or entity including,
without limitation, any regulatory authority or governmental body of the United
States or any state thereof or any political subdivision of the United States or
any state thereof.

         3.7      as of the date hereof no fact or condition exists that would
(or could, with the passage of time, the giving of notice, or both) constitute
an Event of Default under this Agreement or any of the Loan Documents and no
event which has had or could reasonably be expected to have a Material Adverse
Effect has occurred and is continuing. For purposes of this Agreement, "Material
Adverse Effect" means a material adverse effect upon (i) the business,
operations, properties, assets or financial condition of Borrower; or (ii) the
ability of Borrower to perform the Secured Obligations.

Loan and Security Agr.                 -3-

<PAGE>

SECTION 4. INSURANCE AND RISK OF LOSS

         4.1      Risk of loss of, damage to or destruction of the Equipment
shall be borne by the Borrower and effective from the date of this Agreement and
until the payment and performance in full of all Secured Obligations, Borrower
shall at its own expense cause to be carried and maintained all risk casualty
insurance (covering risk of fire, theft and other such risks as the Lender may
require, including standard and extended coverage) with respect to each item of
Equipment in an amount no less than the replacement costs applicable to such
item of Equipment during the term of this Agreement. All policies evidencing
such casualty insurance shall contain a standard mortgagee's endorsement and
shall provide for at least thirty days prior written notice by the underwriter
or insurance company to the Lender in the event of cancellation or expiration.
Borrower shall provide Lender with insurance certificates evidencing the
foregoing at time of closing.

         4.2      If any item of Equipment is lost or rendered unusable as a
result of any physical damage to or destruction of such item of Equipment during
the period from the date hereof to and including the maturity date under the
Note or the date all Secured Obligations hereunder have been fully satisfied,
whichever is later, Borrower shall give to Lender prompt notice thereof.
Borrower shall determine, within fifteen (15) days after the date of occurrence
of such loss, damage or destruction, whether such item of Equipment can be
repaired and restored to the condition in which such item of Equipment was
required to be maintained as of the date immediately preceding such damage. If
Borrower determines that such item of Equipment can be repaired, Borrower, at
its expense, shall cause such item of Equipment to be promptly repaired. If
Borrower determines that such item of I Equipment is lost or cannot be repaired,
Borrower shall promptly notify the Lender and such item of Equipment shall be
deemed to have suffered a "Casualty Loss" for purposes of this Section as of the
date of the occurrence of such loss. Within fifteen (15) days following the
occurrence of any such loss, damage or destruction, Borrower shall notify the
Lender of the item(s) of Equipment which has suffered such Casualty Loss ("Loss
Item"), and within thirty (30) days thereafter (the "Settlement Date"), Borrower
shall either (a) replace such item(s) of Equipment with equipment of the same
model, type and feature configuration, in an operating condition and repair no
less than that required hereunder of the damaged or lost equipment immediately
prior to the date of such damage or loss, and having a fair market value no less
than the Casualty Value (as defined herein) applicable to such item of Equipment
as of the date immediately prior to such damage, in which case such replacement
equipment shall for all purposes hereunder become part of the Collateral and
(without limiting the preceding provisions) Borrower shall grant to Lender a
first lien and security interest in respect of such replacement equipment
pursuant to the terms of this Agreement, and Borrower shall provide the Lender
evidence satisfactory to the Lender of Borrower's good and marketable title to
such replacement equipment (free of any liens, security interests or
encumbrances other than those created by this Agreement and Borrower shall be
entitled to receive the amount of any insurance or other recovery received by
Lender up to cost of obtaining the replacement equipment; or (b) so long as no
Event of Default or event which with the giving of notice or passage of time, or
both, would constitute an Event of Default, has occurred and is continuing,
Borrower may provide substitute equipment satisfactory to Lender to become part
of the Collateral and Borrower shall grant to Lender a first lien and security
interest in respect of such substitute equipment pursuant to the terms of this
Agreement, and Borrower shall provide the Lender evidence satisfactory to Lender
of Borrower's good and marketable title to such substitute equipment (free of
any liens, security interests or

Loan and Security Agr.                 -4-

<PAGE>

encumbrances other than created by this Agreement and Lender shall provide any
required endorsements in connection with any insurance proceeds received by
Borrower pursuant to such insurance policies; or (c) Borrower shall pay Lender
the insurance proceeds payable pursuant to such insurance policies ("Insurance
Proceeds")with respect to such Loss Item(s) and the principal amount of the Note
(and interest accrued on the principal amount so prepayable) shall become due
and payable on the Settlement Date to the extent of the replacement cost for all
such Loss Item(s). For purposes of this Section 4.2, Casualty Value shall mean
an amount equal to the greater of the fair market value of the Equipment as of
the date of the Casualty Loss or the outstanding principal and accrued interest
on the Loan. Moneys so received shall be applied, on the date of such receipt,
as follows: first, to pay any accrued interest on the outstanding principal
amount of the Note on such date; second, to prepay, the outstanding principal
amount of the Note (to the extent of the fair market value attributable to such
Loss Item(s)); third, to pay any other Indebtedness of amounts then due and
owing to the Lender hereunder; and fourth, so long as there has occurred no
Event of Default under Section 8 hereof and no event which with the giving of
notice or passage of time or both would constitute an Event of Default, has
occurred and is continuing, Borrower and Lender hereby agree that the balance of
any such Insurance Proceeds shall be paid promptly to the Borrower.

         4.3      Effective upon the date hereof under the Note and while there
are any Secured Obligations outstanding, Borrower shall cause to be carried and
maintained comprehensive general liability insurance with regard to the
Collateral against risks customarily insured against in the Borrower's business.
Such risks shall include, without limitation, the risks of death, bodily injury
and property damage associated with the Collateral. All policies evidencing such
insurance shall provide for at least thirty (30) days prior written notice by
the underwriter or insurance company to the Lender in the event of cancellation
or expiration.

         4.4      Borrower shall and does hereby indemnify and hold Lender, its
agents and shareholders harmless from and against any and all claims, costs,
expenses, damages and liabilities (including without limitation such claims,
costs, expenses, damages and liabilities based on liability in tort including
without limitation strict liability in tort) including reasonable attorneys'
fees, arising out of Borrower's ownership, possession, operation, control, use,
maintenance, delivery, or other disposition of the Collateral. Notwithstanding
the foregoing, Borrower shall not be responsible under the terms of this Section
4.4 to a party indemnified hereunder for any claims, costs, expenses, damages
and liabilities occasioned by the negligence or willful misconduct of such
indemnified party.

SECTION 5. COVENANTS OF BORROWER

         Borrower covenants and agrees as follows at all times while any of the
Secured Obligations remain outstanding:

         5.1      Borrower shall maintain the Equipment in good operating order,
repair, condition and appearance and protect the Equipment from deterioration,
other than normal wear and tear. Borrower shall not use the Equipment or permit
its use for any purpose other than for which it was designed. Borrower's
obligation regarding the maintenance of the Equipment shall include, without
limitation, all maintenance, repair, refurbishment and replacement recommended
or advised either by the manufacturer, or that commonly performed by prudent
business and/or professional practice. Any exceptions or qualifications
expressed in this Agreement relating to normal or

Loan and Security Agr.                 -5-

<PAGE>

ordinary wear and tear shall not be deemed to limit Borrower's obligations
pursuant to the preceding sentence.

         5.2      Borrower shall only relocate any item of the Collateral
provided that: (a) it shall have caused to be filed and/or delivered to the
Lender all UCC financing statements, certificates or other documents or
instruments necessary to continue in effect the first prior perfected security
interest of the Lender in the Collateral, and (b) it shall have given the Lender
no less than fifteen (15) days prior written notice of such relocation.

         5.3      Upon the request of Lender, Borrower shall, during business
hours, make the Equipment available to Lender for inspection at the place where
it is normally located and shall make Borrower's log and maintenance records
pertaining to the Equipment available to the Equipment available to Lender for
inspection. Borrower shall take all action necessary to maintain such logs and
maintenance records in a correct and complete fashion.

         5.4      Upon the request of Lender, Borrower shall cause the Equipment
to be plainly, permanently and conspicuously marked, by stenciling or by metal
tag or plate affixed thereto, indicating Lender's security interest in the
Equipment. Borrower shall replace any such stenciling, tag or plate which may be
removed or destroyed or become illegible. Borrower shall keep all Equipment free
from any marking or labeling which might be interpreted as a claim of ownership
adverse to Borrower's.

         5.5      Borrower covenants and agrees to pay when due, all taxes, fees
or other charges of any nature whatsoever (together with any related interest or
penalties) now or hereafter imposed or assessed against Borrower, Lender or the
Collateral or upon Borrower's ownership, possession, use, operation or
disposition thereof or upon Borrower's rents, receipts or earnings arising
therefrom. Borrower shall file on or before the due date therefor all personal
property tax returns in respect of the Collateral.

         5.6      Borrower shall furnish to Lender the financial statements
listed hereinafter, prepared in accordance with generally accepted accounting
principles consistently applied (the "Financial Statements"):

                  (a)      as soon as practicable (and in any event within
         thirty (30) days) after the end of each month: an internally prepared
         income statement, balance sheet, and cash flow statement, (including
         the commencement of any material litigation by or against Borrower),
         each certified by Borrower's Chief Executive or Financial Officer to be
         true and correct;

                  (b)      as soon as practicable (and in any event within
         ninety (90) days) after the end of each fiscal year, audited Financial
         Statements, setting forth in comparative form the corresponding figures
         for the preceding fiscal year, and accompanied by any audit report and
         opinion of the independent certified public accountants selected by
         Borrower; and

                  (c)      promptly any additional information (including but
         not limited to tax returns, income statements, balance sheets, and
         names of principal creditors) as Lender reasonably believes necessary
         to evaluate Borrower's continuing ability to meet financial
         obligations.

Loan and Security Agr.                 -6-

<PAGE>

         5.7      Notwithstanding the foregoing, after the effective date of the
initial registration statement covering a public offering of Borrower's
securities, the term "Financial Statements" shall be deemed to refer to only
those statements required by the Securities and Exchange Commission, to be
provided no less frequently than quarterly. Borrower will from time to time
execute, deliver and file, alone or with Lender, any financing statements,
security agreements or other documents; and take all further action that may be
necessary, or that Lender may reasonably request, to confirm, perfect, preserve
and protect the security interests intended to be granted hereby, and in
addition, and for such purposes only, Borrower hereby authorizes Lender to
execute and deliver on behalf of Borrower and to file such financing statements,
security agreement and other documents without the signature of Borrower either
in Lender's name or in the name of Borrower as agent and attorney-in-fact for
Borrower.

         5.8      Borrower shall protect and defend Borrower's title as
well as the interest of the Lender against all persons claiming any interest
adverse to Borrower or Lender and shall at all times keep the Collateral free
and clear from any attachment or levy, liens or encumbrances whatsoever (except
any placed thereon by Lender, or any liens arising by operation of law with
respect to any obligations not yet overdue or any other liens consented to in
writing by Lender) and shall give Lender immediate written notice thereof.

SECTION 6. CONDITIONS PRECEDENT TO LOAN

The obligation of Lender to fund the Loan on each Advance Date(s) shall be
subject to satisfaction by Borrower or waiver by Lender, in Lender's sole
discretion, of the following conditions:

         6.1      (a) The Advance Date(s) for any installment shall occur on or
before December 16, 2000.

         6.2      DOCUMENT DELIVERY. Borrower, on or prior to the Closing Date,
shall have delivered to Lender the following, in form and substance reasonably
satisfactory to Lender:

                  (a)      executed originals of the Agreement, Note(s), Warrant
         Agreement and any documents reasonably required by Lender to effectuate
         the liens of Lender, with respect to all Collateral;

                  (b)      certified copy of resolutions of Borrower's board of
         directors evidencing approval of the borrowing and other transactions
         evidenced by the Loan Documents;

                  (c)      certified copies of the Certificate of Incorporation
         and the Bylaws of Borrower, as amended through the Closing Date;

                  (d)      certificate of good standing for Borrower from its
         state of incorporation and similar certificates from all other
         jurisdictions in which it does business and where the failure to be
         qualified would have a Material Adverse Effect;

                  (e)      such other documents as Lender may reasonably
         request.

         6.3      ADVANCE REQUEST. Borrower, on or prior to each Advance
Date(s), shall have delivered to Lender the following:

Loan and Security Agr.                 -7-

<PAGE>

                  (a)      a minimum of two (2) business days prior to the
         Advance Date(s), written notice in the form of an Advance Request, or
         as otherwise specified by Lender from time to time, specifying amount
         of such Advance and wire transfer instructions;

                  (b)      such other documents as Lender may reasonably
         request.

         6.4      PERFECTION OF SECURITY INTERESTS. Borrower shall have taken or
caused to be taken such actions requested by Lender to grant Lender a first
priority perfected security interest in the Collateral. Such actions shall
include, without limitation, the delivery to Lender of all appropriate financing
statements, executed by Borrower, as to the Collateral granted by Borrower for
all jurisdictions as may be necessary or desirable to perfect the security
interest of Lender in such Collateral

         6.5      ABSENCE OF EVENTS OF DEFAULTS. As of the Closing Date or the
Advance Date, no fact or condition exists that would (or would, with the passage
of time, the giving of notice, or both) constitute an Event of Default under
this Agreement or any of the Loan Documents.

         6.6      MATERIAL ADVERSE EFFECT. As of the Closing Date or the Advance
Date, no event which has had or could reasonably be expected to have a Material
Adverse Effect has occurred and is continuing.

SECTION 7. ASSIGNMENT BY LENDER

         7.1      Borrower acknowledges and understands that Lender may sell and
assign all or a part of its interest hereunder and under the Note and Loan
Documents to any person or entity (an "Assignee"). After such assignment the
term Lender shall mean such Assignee, and such Assignee shall be vested with all
rights, powers and remedies of Lender hereunder with respect to the interest so
assigned; but with respect to any such interest not so transferred, the Lender
shall retain all rights, powers and remedies hereby given. No such assignment by
Lender shall relieve Borrower of any of its obligations hereunder. Borrower
shall acknowledge such assignment or assignments as shall be designated by
written notice given by Lender to Borrower. The Lender agrees that in the event
of any transfer by it of the Note, it will endorse thereon a notation as to the
portion of the principal of the Note which shall have been paid at the time of
such transfer and as to the date to which interest shall have been last paid
thereon.

SECTION 8. DEFAULT

         The occurrence of any one or more of the following events (herein
called "Events of Default") shall constitute a default hereunder and under the
Note:

         8.1      The Borrower defaults in the payment of any principal or
interest payable under this Agreement, the Note or any of the other Loan
Documents and such default continues for more than five (5) days after the due
date thereof;

Loan and Security Agr.                 -8-

<PAGE>

         8.2      The Borrower defaults in the payment or performance of any
other covenant or obligation of the Borrower hereunder or under the Note or any
other Loan Documents for more than ten (10) days after the Lender has given
notice of such default to the Borrower;

         8.3      Any representation or warranty made herein by the Borrower
shall prove to have been false or misleading in any material respect;

         8.4      The making of an assignment by Borrower for the benefit of its
creditors or the admission by Borrower in writing of its inability to pay its
debts as they become due, or the insolvency of Borrower, or the filing by
Borrower of a voluntary petition in bankruptcy, or the adjudication of Borrower
as a bankrupt, or the filing by Borrower of any petition or answer seeking for
itself any reorganization, arrangement, composition, readjustment, liquidation,
dissolution, or similar relief under any present or future statute, law or
regulation, or the filing of any answer by Borrower admitting, or the failure by
Borrower to deny, the material allegations of a petition filed against it for
any such relief, or the seeking or consenting by Borrower to, or acquiescence by
Borrower in, the appointment of any trustee, receiver or liquidator of Borrower
or of all or any substantial part of the properties of Borrower, or the
inability of Borrower to pay its debts when due, or the commission by Borrower
of any act of bankruptcy as defined in the Federal Bankruptcy Act, as amended;

         8.5      The failure by Borrower, within sixty (60) days after the
commencement of any proceeding against Borrower seeking any reorganization,
arrangement, composition, readjustment, liquidation, dissolution or similar
relief under any present or future statute, law or regulation, to obtain the
dismissal of such proceeding or, within sixty (60) days after the appointment,
without the written consent or acquiescence of Lender, of any trustee, receiver
or liquidator of Borrower or of all or any substantial part of the properties of
Borrower, to vacate such appointment; or

         8.6      The default by Borrower under any other notes or other
agreement for borrowed money, lease or other agreement between Borrower and
Lender.

SECTION 9. REMEDIES

         Upon the occurrence hereof of any one or more Events of Default,
Lender, at its option, may declare the Note to be accelerated and immediately
due and payable, (provided, that upon the occurrence of an Event of Default of
the type described in 8.4 or 8.5, the Note and all other Secured Obligations
shall automatically be accelerated and made due and payable without any further
act) whereupon the unpaid principal of and accrued interest on such Note shall
become immediately due and payable, and shall thereafter bear interest at the
Default Rate and calculated in accordance with Section 1.2. Lender may exercise
all rights and remedies with respect to the Collateral granted pursuant hereto
for such Note, or otherwise available to it under applicable law, including the
right to release, hold or otherwise dispose of all or any part of the Collateral
and the right to utilize, process and commingle the Collateral.

         Upon the happening and during the continuance of any Event of Default,
Lender may then, or at any time thereafter and from time to time, apply,
collect, sell in one or more sales, lease or otherwise dispose of, any or all of
the Collateral, in its then condition or following any commercially reasonable
preparation or processing, in such order as Lender may elect, and any such sale
may be made either at public or private sale at its place of business or
elsewhere.

Loan and Security Agr.                 -9-

<PAGE>

Borrower agrees that any such public or private sale may occur upon five (5)
calendar day's notice to Borrower. Lender may require Borrower to assemble the
Collateral and make it available to Lender at a place designated by Lender which
is reasonably convenient to Lender and Borrower. The proceeds of any sale,
disposition or other realization upon all or any part of the collateral shall be
distributed by Lender in the following order of priorities:

         First, to Lender in an amount sufficient to pay in full Lender's
         reasonable costs and professionals' and advisors' fees and expenses;

         Second, to Lender in an amount equal to the then unpaid amount of the
         Secured Obligations in such order and priority as Lender may choose in
         its sole discretion; and

         Finally, upon payment in full of all of the Secured Obligations, to
         Borrower or its representatives or as a court of competent jurisdiction
         may direct.

The Lender shall return to the Borrower any surplus Collateral remaining after
payment of all Secured Obligations.

SECTION 10. MISCELLANEOUS

         10.1     Borrower shall remain liable to Lender for any unpaid Secured
Obligations, advances, costs, charges and expenses, together with interest
thereon and shall pay the same immediately to Lender at Lender's offices.

         10.2     The powers conferred upon Lender by this Agreement are solely
to protect its interest in the Collateral and shall not impose any duty upon
Lender to exercise any such powers.

         10.3     This is a continuing Agreement and the grant of a security
interest hereunder shall remain in full force and effect and all the rights,
powers and remedies of Lender hereunder shall continue to exist until the
Secured Obligations are paid in full as the same become due and payable. When
Borrower has paid in full all Secured Obligations, Lender will execute a written
termination statement, reassigning to Borrower, without recourse, the Collateral
and all rights conveyed hereby and return possession (if Lender has possession)
of the Collateral to Borrower. The rights, powers and remedies of Lender
hereunder shall be in addition to all rights, powers and remedies given by
statute or rule of law and are cumulative. The exercise of any one or more of
the rights, powers and remedies provided herein shall not be construed as a
waiver of any other rights, powers and remedies of Lender. Furthermore,
regardless of whether or not the UCC is in effect in the jurisdiction where such
rights, powers and remedies are asserted, Lender shall have the rights, powers
and remedies of a secured party under the UCC.

         10.4     Upon payment in full of all Secured Obligations, the Lender
shall cancel the Note, this Agreement and all UCC financing statements, if any,
and shall promptly deliver all such canceled documents to the Borrower.

         10.5     GOVERNING LAW. This Agreement, the Note and the other Loan
Documents have been negotiated and delivered to Lender in the State of Illinois
and shall not become effective until accepted by Lender in the State of
Illinois. Payment to Lender by Borrower of the Secured Obligations is due in the
State of Illinois. This Agreement shall be governed by, and

Loan and Security Agr.                 -10-

<PAGE>

construed and enforced in accordance with the laws of the State of Illinois
excluding conflict of laws principles that would cause the application of laws
of any other jurisdiction.

         10.6     CONSENT TO JURISDICTION AND VENUE. All judicial proceedings
arising in or under or related to this Agreement, the Note or any of the other
Loan Documents may be brought in any state or federal court of competent
jurisdiction located in the State of Illinois. By execution and delivery of this
Agreement, each party hereto generally and unconditionally: (a) consents to
personal jurisdiction in Cook County, State of Illinois; (b) waives any
objection as to jurisdiction or venue in the aforesaid courts; and (d)
irrevocably agrees to be bound by any judgment rendered thereby in connection
with this Agreement, the Note and the other Loan Documents. Service of process
on any party hereto in any action arising out of or relating to this Agreement
shall be effective if given in accordance with the requirements for notice set
forth in Section 10.8 below and shall be deemed effective and received as set
forth in Section 10.8 below. Nothing herein shall affect the right to serve
process in any other manner permitted by law or shall limit the right of either
party to bring proceedings in the courts of any other jurisdiction.

         10.7     Whenever possible, each provision of this Agreement shall be
interpreted in such manner as to be effective and valid under applicable law,
but if any provision of this Agreement shall be prohibited by or invalid under
such law, such provision shall be ineffective only to the extent and duration of
such prohibition or invalidity, without invalidating the remainder of such
provision or the remaining provisions of this Agreement.

         10.8     Any notice required or given hereunder shall be deemed
properly given upon the earlier of: (i) the first business day after
transmission by facsimile or hand delivery or deposit with an overnight express
service or overnight mail delivery service; or (ii) or three (3) days after
mailed, postage prepaid, in each case, addressed to the designated recipient at
its address set forth herein or such other address as such party may advise the
other party by notice given in accordance with this provision.

         10.9     Lender and Borrower acknowledge that there are no agreements
or understandings, written or oral, between Lender and Borrower with respect to
the Loan, other than as set forth herein, in the Note and the other Loan
Documents and that this Agreement, the Note and the other Loan Documents contain
the entire agreement between Lender and Borrower with respect thereto. None of
the terms of this Agreement, the Note and the other Loan Documents may be
amended except by an instrument executed by each of the parties hereto.

         10.10    No omission, or delay, by Lender at any time to enforce any
right or remedy reserved to it, or to require performance of any of the terms,
covenants or provisions hereof by Borrower at any time designated, shall be a
waiver of any such right or remedy to which Lender is entitled, nor shall it in
any way affect the right of Lender to enforce such provisions thereafter.

         10.11    All agreements, representations and warranties contained in
this Agreement or the Note, or in any Loan Documents delivered pursuant hereto
or in connection herewith shall be for the benefit of Lender and any Assignee
and shall survive the execution and delivery of this Agreement or the Note and
the expiration or other termination of this Agreement or the Note.

         10.12    This Agreement may be executed in any number of counterparts,
each of which shall be deemed an original, but all such counterparts together
shall constitute but one and the same instrument.

Loan and Security Agr.                 -11-

<PAGE>

         10.13    This Agreement shall be binding upon, and shall inure to the
benefit of, Borrower and its permitted assigns (if any). Borrower shall not
assign its obligations under this Agreement, the Note or any of the other Loan
Documents without Lender's express written consent and any such attempted
assignment shall be void and of no effect. Any assignment by Borrower in
connection with a "Merger" (as defined below) shall be subject to Lender's prior
consent. Any consent granted by Lender shall be conditioned upon such surviving
entity or transferee assuming Borrower's Secured Obligations hereunder pursuant
to assignment documents reasonably acceptable to Lender. If Lender reasonably
withholds its consent to such assignment in connection with a Merger, the
outstanding principal and accrued and unpaid interest shall be prepaid in whole
without a prepayment premium.

         For purposes of this Agreement, a "Merger" shall mean any consolidation
or merger of the Borrower with or into any other corporation or entity, any sale
or conveyance of an or substantially all of the assets or stock of the Borrower
by or to any other person or entity in which Borrower is not the surviving
entity.

         IN WITNESS WHEREOF, the Borrower and the Lender have duly executed and
delivered this Agreement as of the day and year first above written.

                                       BORROWER: CYTOKINETICS, INCORPORATED.

                                             By: /s/ JAMES SABRY
                                                 ---------------------
                                             Title:
                                             Date: _________________

ACCEPTED IN ROSEMONT, ILLINOIS:

                                       LENDER: COMDISCO, INC.

                                             By: /s/ JILL C. HANSES
                                                 --------------------
                                             Title: JILL C. HANSES SENIOR VICE
                                                    PRESIDENT
                                             Date: DEC 23 1999

Loan and Security Agr.                 -12-

<PAGE>

                                   EXHIBIT A-1
                             SECURED PROMISSORY NOTE

                                                          Date: ____________
$______
                                                          Due: _____________

FOR VALUE RECEIVED, Cytokinetics, Inc., Inc. a Delaware corporation (the
"Borrower") hereby promises to pay to the order of Comdisco, Inc., a Delaware
corporation (the "Lender") at P.O. Box 91744, Chicago, IL 60693 or such other
place of payment as the holder of this Secured Promissory Note (this "Note") may
specify from time to time in writing, in lawful money of the United States of
America, the principal amount of ____________________________and 00/100 Dollars
($______________) together with interest at eight and one quarter percent
(8.25%) per annum from the date of this Note to maturity of each installment on
the principal hereof remaining from time to time unpaid, such principal and
interest to be paid 48 equal monthly installments of $___________each,
commencing__________________and on the same day of each month thereafter to and
including_____________ and an additional installment in the amount of $____(15%)
("Balloon Payment")* to be paid on___________________, such installments to be
applied first to accrued and unpaid interest and the balance to unpaid
principal. Interest shall be computed on the basis of a year consisting of
twelve months of thirty days each.

This Note is the Note referred to in, and is executed and delivered in
connection with, that certain Loan and Security Agreement of even date herewith
by and between Borrower and Lender (as the same may from time to time be
amended, modified or supplemented in accordance with its terms, the "Loan
Agreement"), and is entitled to the benefit and security of the Loan Agreement
and the other Loan Documents (as defined in the Loan Agreement), to which
reference is made for a statement of all of the terms and conditions thereof.
All terms defined in the Loan Agreement shall have the same definitions when
used herein, unless otherwise defined herein. Attached hereto as Exhibit B is a
list of Collateral which is being financed with the proceeds of the Loan
evidenced by this Note, which Collateral shall be deemed to be listed on Exhibit
B to the Loan Agreement.

The Borrower waives presentment and demand for payment, notice of dishonor,
protest and notice of protest and any other notice as permitted under the UCC or
any applicable law.

This Note has been negotiated and delivered to Lender and is payable in the
State of Illinois, and shall not become effective until accepted by Lender in
the State of Illinois. This Note shall be governed by and construed and enforced
in accordance with, the laws of the State of Illinois, excluding any conflicts
of law rules or principles that would cause the application of the laws of any
other jurisdiction.

        BORROWER:                          CYTOKINETICS, INC.
                                           280 East Grand Ave
                                           South San Francisco, CA 94080

                                           Signature: _________________________

                                           Print Name: ________________________

                                           Title: ______________________________

* Borrower may request Lender to finance the Balloon Payment over 12 months at
8%. In that case a new promissory note will be prepared.

                                      -1-

<PAGE>

                                   EXHIBIT A-2
                             SECURED PROMISSORY NOTE

                                                          Date: ____________
$______
                                                          Due: _____________

FOR VALUE RECEIVED, Cytokinetics, Inc., Inc. a Delaware corporation (the
"Borrower") hereby promises to pay to the order of Comdisco, Inc., a Delaware
corporation (the "Lender") at P.O. Box 91744, Chicago, IL 60693 or such other
place of payment as the holder of this Secured Promissory Note (this "Note") may
specify from time to time in writing, in lawful money of the United States of
America, the principal amount of ____________________________and 00/100 Dollars
($ _______) together with interest at eight and one quarter percent (8.25%) per
annum from the date of this Note to maturity of each installment on the
principal hereof remaining from time to time unpaid, such principal and interest
to be paid 36 equal monthly installments of $__________each,
commencing__________________and on the same day of each month thereafter to and
including____________ and an additional installment in the amount of $____(15%)
("Balloon Payment")* to be paid on _______, such installments to be applied
first to accrued and unpaid interest and the balance to unpaid principal.
Interest shall be computed on the basis of a year consisting of twelve months of
thirty days each.

This Note is the Note referred to in, and is executed and delivered in
connection with, that certain Loan and Security Agreement of even date herewith
by and between Borrower and Lender (as the same may from time to time be
amended, modified or supplemented in accordance with its terms, the "Loan
Agreement"), and is entitled to the benefit and security of the Loan Agreement
and the other Loan Documents (as defined in the Loan Agreement), to which
reference is made for a statement of all of the terms and conditions thereof.
All terms defined in the Loan Agreement shall have the same definitions when
used herein, unless otherwise defined herein. Attached hereto as Exhibit B is a
list of Collateral which is being financed with the proceeds of the Loan
evidenced by this Note, which Collateral shall be deemed to be listed on Exhibit
B to the Loan Agreement.

The Borrower waives presentment and demand for payment, notice of dishonor,
protest and notice of protest and any other notice as permitted under the UCC or
any applicable law.

This Note has been negotiated and delivered to Lender and is payable in the
State of Illinois, and shall not become effective until accepted by Lender in
the State of Illinois. This Note shall be governed by and construed and enforced
in accordance with, the laws of the State of Illinois, excluding any conflicts
of law rules or principles that would cause the application of the laws of any
other jurisdiction.

        BORROWER:                          CYTOKINETICS, INC.
                                           280 East Grand Ave
                                           South San Francisco, CA 94080

                                           Signature: _________________________

                                           Print Name: ________________________

                                           Title: _____________________________

* Borrower may request Lender to finance the Balloon Payment over 12 months at
8%. In that case a new promissory note will be prepared.

                                      -1-

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