Document:

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                                                                    Exhibit 4.13

         THIS SECURITY HAS NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933,
AS AMENDED (THE "ACT") AND MAY NOT BE OFFERED, SOLD OR OTHERWISE TRANSFERRED,
PLEDGED OR HYPOTHECATED UNLESS AND UNTIL REGISTERED UNDER THE ACT OR AN
EXEMPTION FROM THE REGISTRATION REQUIREMENTS OF THE ACT IS AVAILABLE FOR SUCH
OFFER, SALE, OR TRANSFER, PLEDGE OR HYPOTHECATION IN THE OPINION OF LEGAL
COUNSEL REASONABLY SATISFACTORY TO THE COMPANY.

                                     WARRANT

                      To Purchase Shares of Common Stock of
                               CYTOKINETICS, INC.

         THIS CERTIFIES that, for value received Slough Estates USA Inc., a
Delaware corporation (the "Holder"), is entitled, upon the terms and subject to
the conditions hereinafter set forth, at any time after the date hereof and
prior to the Commencement Date (as defined below), to subscribe for and purchase
from Cytokinetics, Inc., a Delaware corporation (the "Company"), 180,000 shares
of the Company's Common Stock at an exercise price ("Exercise Price") of $0.29
per share, subject to adjustment as set forth below.

         1. Title of Warrant. Prior to the expiration hereof and subject to
compliance with applicable laws, this Warrant and all rights hereunder are
transferable, in whole or in part, at the office or agency of the Company,
referred to in Section 2 hereof, by the holder hereof in person or by duly
authorized attorney, upon surrender of this Warrant together with the Assignment
Form annexed hereto properly endorsed.

         2. Exercise of Warrant. The purchase rights represented by this Warrant
are exercisable by the registered holder hereof, in whole or in part, at any
time after the effective date of the assignment and assumption to and by the
Company of that certain Lease, dated April 13, 1998 (as amended) by and between
MetaXen, LLC and Britannia Pointe Grand Limited Partnership ("BPGLP") and prior
to the date that is five (5) years after the closing date of an underwritten
initial public offering ("IPO") of the Company's Common Stock pursuant to a
registration statement filed with the Securities and Exchange Commission (the
"SEC") under the Act, subject to adjustment as hereinafter provided, by the
surrender of this Warrant and the Notice of Exercise Form annexed hereto duly
executed at the office of the Company, in South San Francisco, California (or
such other office or agency of the Company as it may designate by notice in
writing to the registered holder hereof at the address of such holder appearing
on the books of the Company), and upon payment of the Exercise Price for the
shares thereby purchased (i) by cash or check or bank draft payable to the order
of the Company, (ii) by cancellation of indebtedness of the Company payable to
the holder hereof at the time of exercise, or (iii) by delivery of an election
in writing to receive a number of shares of Common Stock equal to the aggregate
number of shares of Common Stock subject to this Warrant (or the portion thereof
being cancelled upon such exercise), less that number of shares of Common Stock
having a fair market value as of such date equal to the aggregate Exercise Price
of the Warrant (or such

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portion thereof); whereupon the holder of this Warrant shall be entitled to
receive a certificate for the number of shares so purchased. The Company agrees
that if at the time of the surrender of this Warrant and purchase the holder
hereof shall be entitled to exercise this Warrant, the shares so purchased shall
be and be deemed to be issued to such holder as the record owner of such shares
as of the close of business on the date on which this Warrant shall have been
exercised as aforesaid. For purposes of clause (iii) of the preceding sentence,
the fair market value of one share of the Company's Common Stock shall be
determined as follows: (1) if the Company's Common Stock is listed on a national
stock exchange, on the NASDAQ National Market System or on any other
over-the-counter market, then such fair market value shall be the closing price
per share reported for such class on such national stock exchange or on the
NASDAQ National Market System, or the average of the final "bid" and "asked"
prices reported on such over-the-counter market, as applicable, at the close of
business on the date of calculation, as reported in the Wall Street Journal; and
(2) if the Company's Common Stock is not listed on any national stock exchange,
on the NASDAQ National Market System or on any other over-the-counter market,
then the Board of Directors of the Company shall determine such fair market
value as of the date of calculation in its reasonable good faith judgment, and
shall (upon written request by the holder hereof) advise the holder hereof of
such determination prior to any decision by such holder to exercise its purchase
rights under this Warrant.

         Certificates for shares purchased hereunder shall be delivered to the
holder hereof within a reasonable time, but not later than ten (10) days, after
the date on which this Warrant shall have been exercised as aforesaid.

         If this Warrant is exercised with respect to less than all of the
shares covered hereby, the holder hereof shall be entitled to receive a new
Warrant, in this form, covering the number of shares with respect to which this
Warrant shall not have been exercised.

         The Company covenants that all shares of stock which may be issued upon
the exercise of rights represented by this Warrant will, upon exercise of the
rights represented by this Warrant, be duly authorized, validly issued, fully
paid and nonassessable and free from all taxes, liens and charges in respect of
the issue thereof (other than taxes in respect of any transfer occurring
contemporaneously with such issue).

         3. No Fractional Shares or Scrip. No fractional shares or scrip
representing fractional shares shall be issued upon the exercise of this
Warrant.

         4. Charges, Taxes and Expenses. Issuance of certificates for shares of
Common Stock upon the exercise of this Warrant shall be made without charge to
the holder hereof for any issue or transfer tax or other incidental expense in
respect of the issuance of such certificate, all of which taxes and expenses
shall be paid by the Company, and such certificates shall be issued in the name
of the holder of this Warrant or in such name or names as may be directed by the
holder of this Warrant; provided, however, that in the event certificates for
shares of Common Stock are to be issued in a name other than the name of the
holder of this Warrant, this Warrant when surrendered for exercise shall be
accompanied by the Assignment Form attached hereto duly executed by the holder
hereof; and provided further, that upon any transfer involved in the issuance or
delivery of any

                                      -2-
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certificates for shares of Common Stock, the Company may require, as a condition
thereto, the payment of a sum sufficient to reimburse it for any transfer tax
incidental thereto.

         5. No Rights as Shareholders. This Warrant does not entitle the holder
hereof to any voting rights or other rights as a shareholder of the Company
prior to the exercise hereof. Notwithstanding the foregoing, the Company shall,
upon written request by the holder hereof to the chief financial officer of the
Company from time to time (but not more often than twice in any 12-month period)
provide to such holder copies of the following documents within a reasonable
time after such request (but in all events only to the extent that, and no
sooner than the time that, such documents have been made available to the
Company's shareholders): (i) the Company's most recent audited annual financial
statements or, if audited statements are not available, then the Company's
unaudited annual financial statements as of the end of the Company's most
recently ended fiscal year and (ii) unaudited quarterly financial statements for
each quarter of the Company's fiscal year since the date of the annual financial
statements delivered pursuant to clause (i) above. Notwithstanding the preceding
sentence, during any period in which the Company has outstanding a class of
publicly-traded securities or is for any other reason reporting company under
the Securities Exchange Act of 1934, it shall be sufficient compliance with any
information request from the holder hereof pursuant to such sentence for the
Company to provide copies of its most recent Form 10-K and annual report, any
Form 10-Qs and/or Form 8-Ks filed by the Company with the SEC since the date of
such Form 10-K, and any proxy statements.

         6. Exchange and Registry of Warrant. This Warrant is exchangeable, upon
the surrender hereof by the registered holder at the above-mentioned office or
agency of the Company, for a new Warrant of like tenor and dated as of such
exchange.

         The Company shall maintain at the above-mentioned office or agency a
registry showing the name and address of the registered holder of this Warrant.
This Warrant may be surrendered for exchange, transfer or exercise, in
accordance with its terms, at such office or agency of the Company, and the
Company shall be entitled to rely in all respects, prior to written notice to
the contrary, upon such registry.

         7. Loss, Theft, Destruction or Mutilation of Warrant. Upon receipt by
the Company of evidence reasonably satisfactory to it (such as an affidavit of
the holder hereof) of the loss, theft, destruction or mutilation of this
Warrant, and in case of loss, theft or destruction, of indemnity or security
reasonably satisfactory to it, and upon reimbursement to the Company of all
reasonable expenses incidental thereto, and upon surrender and cancellation of
this Warrant, if mutilated, the Company will make and deliver a new Warrant of
like tenor and dated as of such cancellation, in lieu of this Warrant.

         8. Saturdays, Sundays, Holidays, etc. If the last or appointed day for
the taking of any action or the expiration of any right required or granted
herein shall be a Saturday or a Sunday or shall be a legal holiday, then such
action may be taken or such right may be exercised on the next succeeding day
not a legal holiday.

                                      -3-
<PAGE>

         9. Adjustment. The number of shares for which this Warrant is
exercisable and the time period for exercise are subject to adjustment from time
to time as follows:

                  (a) Reclassification, etc. If the Company at any time shall,
by subdivision, combination or reclassification of securities or otherwise,
change any of the securities to which purchase rights under this Warrant exist
into the same or a different number of securities of any class or classes, this
Warrant shall thereafter be 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 under this Warrant
immediately prior to such subdivision, combination, reclassification or other
change and the Exercise Price shall be proportionately adjusted.

                  (b) Cash Distributions. No adjustment on account of cash
dividends or interest on the Company's Common Stock or other securities
purchasable hereunder will be made to the Exercise Price.

                  (c) This warrant shall be deemed rescinded in the event that
the Company's assumption of that certain Lease, dated April 13, 1998 (as
amended) by and between BPGLP and MetaXen, LLC shall not have occurred by
September 30, 2000.

         10. Miscellaneous.

                  (a) Termination Upon Merger, Sale of Assets, etc. If at any
time after the date hereof the Company proposes to merge with or into any other
corporation, effect a consolidation or reorganization with or into any other
entity, or sell or convey all or substantially all of its assets to any other
entity (collectively, a "Merger"), the Company shall give the Holder written
notice ("Merger Notice") of such impending transaction not later than thirty
(30) days prior to the closing of such transaction. The Merger Notice shall
describe the material terms and conditions of the impending transaction,
including the aggregate value of consideration to be received by the Holder for
the shares underlying this Warrant on an as exercised basis, and the Company
shall thereafter give the Holder prompt notice of any material changes to such
terms and conditions.

                           (i) If, pursuant to such Merger, the shareholders of
the Company receive solely cash and/or publicly traded securities in exchange
for their shares of stock in the Company, as stated in the Merger Notice, and
this Warrant has not been exercised prior to the closing of such transaction,
this Warrant shall terminate.

                           (ii) Notwithstanding anything to the contrary, if,
pursuant to such Merger, the shareholders of the Company receive non-publicly
traded securities in exchange for their shares of stock in the Company, or if
the aggregate value of the consideration consisting of cash and/or publicly
traded securities to be received by the Holder for the securities underlying
this Warrant, as stated in the Merger Notice, does not equal or exceed the
aggregate Exercise Price of such underlying securities, then this Warrant shall
not terminate pursuant to the provisions of Section 10(a)(i) above, and the
Company shall, as a condition precedent to such transaction, cause effective
provisions to be made so that the holder hereof shall have the right thereafter,
by exercising this Warrant (in lieu of the shares of the common stock of the
Company immediately theretofore

                                      -4-
<PAGE>

purchasable and receivable upon exercise of this Warrant) to purchase the kind
and amount of shares of stock and other securities and property (including cash)
receivable upon such transaction. Any such provision shall include provisions
for adjustments in respect of such shares of stock and other securities and
property that shall be as nearly equivalent as may be practicable to the
adjustments provided for in this Warrant. The foregoing provisions of this
Section 10(a)(ii) shall similarly apply to successive transactions, unless this
Warrant is first terminated pusuant to the provisions of Section 10(a)(i) above.

                  (b) Issue Date. The provisions of this Warrant shall be
construed and shall be given effect in all respect as if it had been issued and
delivered by the Company on the date hereof. This Warrant shall be binding upon
any successors or assigns of the Company. This Warrant shall constitute a
contract under the laws of the State of California and for all purposes shall be
construed in accordance with and governed by the laws of said state.

                  (c) Restrictions. The holder hereof acknowledges that the
Common Stock acquired upon the exercise of this Warrant shall have restrictions
upon its resale imposed by state and federal securities laws.

                  (d) Authorized Shares. The Company covenants that during the
period the Warrant is exercisable, it will reserve from its authorized and
Unicode Common Stock a sufficient number of shares to provide for the issuance
of Common Stock upon the exercise of any purchase rights under this Warrant. The
Company further covenants that its issuance of this Warrant shall constitute
full authority to its officers who are charged with the duty of executing stock
certificates to execute and issue the necessary certificates for shares of the
Company's Common Stock upon the exercise of the purchase rights under this
Warrant.

                  (e) No Impairment. The Company will not, by amendment of its
Articles of Incorporation or any other voluntary action, avoid or seek to avoid
the observance or performance ot 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 action as may be necessary or appropriate in order to protect
the rights of the holder hereof against impairment.

                  (f) Notices of Record Date. In case:

                           (i) the Company shall take a record of the holders of
its Common Stock for the purposes of entitling them to receive any dividend
(other than a cash dividend) or other distribution, or any right to subscribe
for, purchase or otherwise acquire any shares or stock of any class or any other
securities or property, or to receive any other right; or

                           (ii) of any capital reorganization of the Company,
any reclassification of the capital stock of the Company, any consolidation or
merger of the Company with or into another corporation, or any conveyance of all
or substantially all of the assets of the Company to another corporation; or

                                      -5-
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                           (iii) of the voluntary or involuntary dissolution,
liquidation or winding-up of the Company;

         then, and in each such case, the Company will mail or cause to be
mailed to the holder of this Warrant a notice specifying, as the case may be,
(i) the date on which a record is to be taken for the purpose of such dividend,
distribution or right, and stating the amount and character of such dividend,
distribution or right, or (ii) the date on which such reorganization,
reclassification, consolidation, merger, conveyance, dissolution, liquidation or
winding-up is to take place, and the time, if any is to be fixed, as of which
the holders of record of Common Stock shall be entitled to exchange their shares
of Common Stock for securities or other property deliverable upon such
reorganization, reclassification, consolidation, merger, conveyance,
dissolution, liquidation or winding-up. Such notice shall be mailed at least
thirty (30) days prior to the date therein specified.

                  (g) Attorneys' Fees. In any litigation, arbitration or other
legal proceeding between the Company and the holder hereto relating to or
arising out of this Warrant, the prevailing party shall be entitled to recover
all its fees, costs and expenses incurred in connection with such proceeding,
including (but not limited to) reasonable fees and expenses of attorneys and
accountants and including (but not limited to) all such fees, costs and expenses
incurred in connection with any appeals and/or in connection with the
enforcement of any judgment or award rendered in such proceeding.

                                      -6-
<PAGE>

         IN WITNESS WHEREOF, Cytokinetics, Inc. has caused this Warrant to be
executed by its officers thereunto duly authorized.

Dated: July 20, 1999

CYTOKINETICS, INC.

By: /s/ James Sabry
   ----------------------------
Title: CEO & President

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<PAGE>

                               NOTICE OF EXERCISE

         To: CYTOKINETICS, INC.

         (1) ____________________, the undersigned, hereby elects to
purchase____________________________shares of Common Stock (the "Shares") at an
exercise price of $0.29 per share of Cytokinetics, Inc. pursuant to the terms of
the attached Warrant, and tenders herewith payment of the aggregate purchase
price of $____________in full (if exercising pursuant to net exercise
provisions, enter $-0-), together with all applicable transfer taxes, if any:

                  (choose one)

                  [ ]      By cash, check or sale draft payable to Cytokinetics,
                           Inc.; or

                  [ ]      By cancellation of indebtedness of Cytokinetics,
                           Inc., payable to the undersigned as of the date
                           hereof; or

                  [ ]      By net exercise pursuant to the provisions of Secton
                           2(iii) of the attached warrant (no tender of payment
                           for the Shares needed).

         (2) Please issue a certificate or certificates representing the Shares
(or the number of shares of Common Stock remaining after application of the net
exercise provisions of Section 2 (iii) of the attached warrant) in the name of
the undersigned or in such other name as is specified below:

         __________________________
         (Name)

         __________________________

         __________________________
         (Address)

         (3) The undersigned represents that the aforesaid shares of Common
Stock are being acquired for the account of the undersigned for investment and
not with a view to, or for resale in connection with, the distribution thereof
and that the undersigned has no present intention of distributing or reselling
such shares.

         _________________________________________________________
         (Date) (Signature)

                                      -8-
<PAGE>

                                 ASSIGNMENT FORM

(To assign the foregoing warrant, execute this form and supply required
information. Do not use this form to purchase shares.)

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

         _________________________________________
         (Please Print)

         whose address is    _____________________

                             _____________________
                             (Please Print)

         Dated:_____________________,__________.

         Holder's Signature:___________________

         Holder's Address:  ___________________

                            ___________________

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

                                      -9-<PAGE>

                                                                    Exhibit 4.14

THE SECURITIES REPRESENTED HEREBY HAVE NOT BEEN REGISTERED UNDER THE UNITED
STATES SECURITIES ACT OF 1933, AS AMENDED (THE "SECURITIES ACT"). THESE
SECURITIES MAY BE OFFERED, SOLD OR OTHERWISE TRANSFERRED ONLY (A) TO THE
CORPORATION, (B) OUTSIDE THE UNITED STATES IN ACCORDANCE WITH RULE 901 OR
REGULATIONS UNDER THE SECURITIES ACT IF APPLICABLE, OR (C) INSIDE THE UNITED
STATES (i) PURSUANT TO THE EXEMPTION FROM REGISTRATION PROVIDED BY RULE 144
THEREUNDER, IF APPLICABLE, AND IN ACCORDANCE WITH APPLICABLE STATE SECURITIES
LAWS OR (ii) IN COMPLIANCE WITH ANOTHER APPLICABLE EXEMPTION UNDER THE
SECURITIES ACT AND ANY APPLICABLE STATE SECURITIES LAWS, SUCH COMPLIANCE, AT THE
OPTION OF THE CORPORATION, TO BE EVIDENCED BY AN OPINION OF COUNSEL, IN FORM
ACCEPTABLE TO THE CORPORATION, THAT NO VIOLATION OF SUCH REGISTRATION PROVISIONS
WOULD RESULT FROM ANY PROPOSED TRANSFER OR ASSIGNMENT.

No. W-_________ SERIES B PREFERRED STOCK PURCHASE WARRANT As of August 30, 1999
                           CYTOKINETICS, INCORPORATED

         THIS CERTIFIES that, for value received, The Magnum Trust (the
"Holder") or its assigns, is entitled to subscribe for and purchase, from
Cytokinetics, Incorporated, a Delaware corporation (the "Company"), shares of
the Company's Series B Preferred Stock, upon the terms and subject to the
conditions set forth herein, at any time on or after the date of this Warrant,
and on or before, but in no case after August 30, 2006.

         1.       Exercise Price; Number of Warrant Shares. The purchase price
of one share of Series B Preferred Stock under this Warrant shall be $2.90 per
share, subject to adjustment pursuant to Sections 7 and 8 (such price as it
shall be adjusted, the "Exercise Price"). The number of shares of Series B
Preferred Stock purchasable upon exercise of this Warrant is 100,000, which
shares upon such purchase shall be fully paid and non-assessable (the "Warrant
Shares").

         2.       Exercise, of Warrant.

                  (a)      Exercise Procedure. The purchase rights represented
by this Warrant are exercisable by the Holder or its assignee, in whole or in
part, at any time before August 30, 2006, by the surrender of this Warrant and a
Notice of Exercise in the form attached as Exhibit A duly executed at, the
office of the Company in South San Francisco, California (or such other office
or agency of the Company as it may designate by notice in writing to the Holder
at the address of such holder appearing on the books of the Company), and upon
payment of the Exercise Price of the shares thereby purchased (by cash or by
check or bank draft payable to the order of the Company or by cancellation of
indebtedness of the Company to the holder, if any, at the time of exercise in an
amount equal to the Exercise Price of the shares thereby purchased or pursuant
to the net exercise proceeding set forth in Section 2(b), below); whereupon the
Holder shall be entitled to receive a certificate for the number of shares of
Series B Preferred Stock so purchased. If this Warrant is exercised as to only a
portion of the shares for which it is exercisable, the Company shall, upon such
exercise, deliver to the Holder a new Warrant representing the remaining shares
for which the Warrant shall then be exercisable. This Warrant shall be deemed to
have been exercised

<PAGE>

immediately prior to the close of business on the date of delivery of such
Notice of Exercise and payment as provided above, and the person entitled to
receive the shares issuable upon such exercise shall be treated for all purposes
as the holder of such shares of record as of the close of business on such date.
As promptly as practicable on or after such date, the Company shall issue and
deliver to such person a certificate for the number of shares issuable upon such
exercise.

                  (b)      Net Exercise.

                           (1)      In lieu of the cash payment set forth in
Section 2(a) above, the Holder shall have the right ("Conversion Right") to
convert this Warrant or any portion thereof (without payment of any kind) into
that number of shares of Series B Preferred Stock equal to (i) the product of
(A) the number of shares of Series B Preferred then issuable upon such whole or
partial exercise of this Warrant and (B) the excess, if any, of (X) the Market
Price Per Share (as determined pursuant to Section 2(b)(3) below) with respect
to the date of conversion over (Y) the Exercise Price in effect on the business
day next preceding the date of conversion, divided by (ii) the Market Price Per
Share with respect to the date of conversion.

                           (2)      Manner of Conversion. The conversion rights
provided for in this Section 2(b) may be exercised in whole or in pan and at any
time and from time to time while any portion of this Warrant remains
outstanding. In order to exercise its conversion rights under this Section, the
Holder shall surrender to the Company, at its offices, this Warrant certificate
accompanied by a duly completed Notice of Conversion in the form annexed hereto
as Exhibit B. The Warrant (or so much thereof as shall have been surrendered for
conversion) shall be deemed to have been converted immediately prior to the
close of business on the day of surrender of such Warrant certificate for
conversion in accordance with the foregoing provisions. As promptly as
practicable on or after the conversion date, the Company shall issue and shall
deliver to the Warramholder (i) a certificate or certificates representing the
number of shares of Series B Preferred to which the Warrantholder shall be
entitled as a result of the conversion, and (ii) if the Warrant certificate is
being converted in part only, a new certificate of like tenor and date for the
balance of the unconverted portion of the Warrant certificate.

                           (3)      Market Price Per Share. As used herein, the
"Market Price Per Share" on any date shall mean the fair market value of each
share of Series B Preferred Stock as determined in good faith by the Board of
Directors of the Company, provided that, after the Company's registration and
sale of shares of its Common Stock pursuant to a public offering, the term
"Market Price Per Share" shall mean the closing price per share of the Company's
Common Stock for the trading day immediately preceding the date of exercise. The
closing price for each such day shall be the last sale price or, in case no such
sale takes place on such day, the average of the closing bid and asked prices,
in either case on the principal securities exchange on which the shares of such
Common Stock of the Company are listed or admitted to trading or, if applicable,
the last sale price, or, in case no sale takes place on such day, the average of
the closing bid and asked prices of such Common Stock on NASDAQ or any
comparable system, or if such Common Stock is not reported on NASDAQ, or a
comparable system, the average of the closing bid and asked prices as furnished
by two members of the National Association of Securities Dealers, Inc. selected
from time to time by the Company for that purpose. If such bid and asked prices
are not available, then "Market Price Per

                                      -2-

<PAGE>

Share" shall be equal to the fair market value of such Common Stock as
determined in good faith by the Board of Directors of the Company.

         3.       Restrictions on Transfer.

                  (a)      Investment Representation. The Holder agrees that the
Holder will not offer, sell or otherwise dispose of this Warrant or any
securities issued on exercise of this Warrant except under circumstances which
will not result in a violation of the Securities Act. Upon exercise of this
Warrant, the Holder shall confirm in writing, by executing the form attached as
Exhibit C hereto, that the securities purchased thereby are being acquired for
investment solely for the Holder's own account and not as a nominee for any
other Person, and not with a view toward distribution or resale.

                  (b)      Certificate Legends. This warrant and all securities
issued upon exercise of this Warrant (unless registered under the Securities
Act) shall be stamped or imprinted with a legend in substantially the following
form (in addition to any legends required by applicable state securities laws):

         THE SHARES REPRESENTED BY THIS CERTIFICATE HAVE BEEN ACQUIRED FOR
         INVESTMENT AND NOT WITH A VIEW TO, OR IN CONNECTION WITH, THE SALE OR
         DISTRIBUTION THEREOF, NO SUCH SALE OR DISPOSITION MAY BE EFFECTED
         WITHOUT AN EFFECTIVE REGISTRATION STATEMENT RELATED THERETO OR AN
         OPINION OF COUNSEL SATISFACTORY TO THE COMPANY THAT SUCH REGISTRATION
         IS NOT REQUIRED UNDER THE SECURITIES ACT OF 1933.

         THE SHARES REPRESENTED BY THIS CERTIFICATE MAY BE TRANSFERRED ONLY IN
         ACCORDANCE WITH THE TERMS OF AN AGREEMENT BETWEEN THE COMPANY AND THE
         STOCKHOLDER, A COPY OF WHICH IS ON FILE WITH THE SECRETARY OF THE
         COMPANY.

                  (c)      Disposition of Warrant or Shares. With respect to any
offer, sale or other disposition of this Warrant or any securities issued upon
exercise of this Warrant before an initial public offering, the Holder agrees to
give written notice to the Company prior thereto, describing briefly the manner
thereof, together with a written opinion of the Holder's counsel, if reasonably
requested by the Company, to the effect that such offer, sale or other
disposition may be effected without registration under the Securities Act or
qualification under any applicable state securities laws of this Warrant or such
shares, as the case may be, and indicating whether or not under the Securities
Act certificates for this Warrant or such shares, as the case may be, to be sold
or otherwise disposed of require any restrictive legend as to applicable
restrictions on transferability in order to insure compliance with the
Securities Act. Each certificate representing this Warrant or the securities
thus transferred (except a transfer pursuant to Rule 144) shall bear a legend as
to the applicable restrictions on transferability in order to insure compliance
with the Securities Act, unless in the aforesaid reasonably satisfactory opinion
of counsel for the Holder or the security holder, as the case may be, such
legend is not necessary in order to insure compliance with the Securities Act.
The Company may issue stop transfer instructions to its transfer agent in
connection with such restriction.

                                       -3-

<PAGE>

                  4.       No Rights as Shareholder. This Warrant does not
entitle the Holder to any voting rights or other rights as a shareholder of the
Company prior to exercise; provided, however, that the Holder shall have
"piggy-back" registration rights equivalent to those given to holders of Series
B Preferred Stock pursuant to that certain First Amended and Restated Investors'
Rights Agreement dated August 30,1999 by and among such holders and the Company,
as the same may be amended from time to time (the "Rights Agreement"), and,
provided further, that the Holder shall be bound by the transfer restrictions
set forth in the Rights Agreement, including, without limitation, the Market
Stand-Off provisions contained therein.

                  5.       Loss. Theft, Destruction or Mutilation of Warrant.
Upon receipt by the Company of evidence reasonably satisfactory to it of the
loss, theft, destruction or mutilation of this Warrant, and in case of loss,
theft or destruction, of indemnity reasonably satisfactory to it, and upon
reimbursement to the Company of all reasonable expenses incidental thereto, and
upon surrender and cancellation of this Warrant, if mutilated, the Company shall
make and deliver a new Warrant of like tenor in lieu of this Warrant.

                  6.       Saturdays, Sundays, Holidays, etc. If the last or
appointed day for the taking of any action or the expiration of any right
required or granted herein shall be a Saturday or a Sunday or shall be a legal
holiday, then such action may be taken or such right may be exercised on the
next succeeding day not a legal holiday.

                  7.       Change of Control, Qualified IPO and Anti-Dilution.

                           (a)      Merger, Sale of Assets, etc. If at any time
after the date hereof the Company proposes to merge with or into any other
corporation, effect a consolidation or acquisition with or into any other
entity, which merger, consolidation or acquisition is of 100% of the voting
securities of the Company (a "Termination Transaction"), the Company shall give
the Holder written notice ("Merger Notice") of such impending transaction not
later than thirty (30) days prior to the closing of such transaction. The Merger
Notice shall describe the material terms and conditions of the impending
transaction, including the price and aggregate value of securities and other
consideration to be received by holders of Series B Preferred stock, by holders
of Common Stock and by the Holder for the shares underlying this Warrant on an
as exercised basis, and the Company shall thereafter give the Holder prompt
notice of any material changes to such terms and conditions. If this Warrant has
not been exercised or converted prior to the closing of a Termination
Transaction that is the subject of such a Merger Notice, this Warrant shall
terminate. Notwithstanding anything to the contrary in this Section 7(a), if,
after the closing of a Termination Transaction, the shareholders of the Company
prior to the closing will hold securities representing more than 50% of the
voting control of the surviving entity, this warrant shall not terminate. In the
event of such a non-terminating transaction, and in the event of a transaction
of the sale or conveyance of all or substantially all of the assets of the
Company, the Company shall, as a condition precedent to such transaction, cause
effective provisions to be made so that the holder hereof shall have the right
thereafter, by exercising this Warrant (in lieu of the shares of the common
stock of the Company immediately theretofore purchasable and receivable upon
exercise of this Warrant) to purchase the kind and amount of shares of stock and
other securities and property (including cash) receivable upon such transaction
by any holders of Series B Preferred Stock or holders of Common Stock, as
applicable. Any such provision shall include provisions for adjustments in
respect of such shares of

                                      -4-

<PAGE>

stock and other securities and property that shall be as nearly equivalent as
may be practicable to the adjustments provided for in this Warrant. The
foregoing provisions of this Section 7(a) shall similarly apply to successive
transactions, unless this Warrant is first terminated pursuant this Section
7(a).

                  (b)      Splits and Combinations. If the Company at any time
subdivides any of its outstanding shares of Series B Preferred Stock into a
greater number of shares, the Exercise Price in effect immediately prior to such
subdivision shall be proportionately reduced, and conversely, if the outstanding
shares of Series B Preferred Stock are combined into a smaller number of shares,
the Exercise Price in effect immediately prior to such combination shall be
proportionately increased. Upon any adjustment of the Exercise Price under this
Section 7(b), the number of shares of Series B Preferred Stock issuable upon
exercise of this Warrant shall equal the number of shares determined by dividing
(i) the aggregate Exercise Price payable for the purchase of all shares issuable
upon exercise of this Warrant immediately prior to such adjustment by (ii) the
Exercise Price per share in effect immediately after such adjustment.

                  (c)      Reclassifications. If the Company changes any of the
securities as to which purchase rights under this Warrant exist into the same or
a different number of securities of any other class or classes, this Warrant
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 that were subject to the purchase rights under this Warrant
immediately prior to such reclassification or other change and the Exercise
Price therefor shall be appropriately and proportionately adjusted.

                  (d)      Dividends and Distribution. If the Company declares
a non-cash dividend or other distribution on the Series B Preferred Stock or the
Company's Common Stock or if a dividend or other distribution on the Series B
Preferred Stock or the Company's Common Stock occurs (other than a cash
dividend) then, as part of such dividend or distribution, lawful provision shall
be made so that there shall thereafter be deliverable upon the exercise of this
Warrant or any portion thereof, in addition to the number of shares of Series B
Preferred Stock receivable thereupon and without payment of any additional
consideration, the amount of the dividend or other distribution to which the
holder of the number of shares of Series B Preferred Stock obtained upon
exercise hereof, and the holder of the number of shares of Common Stock into
which such Series B Preferred Stock shall be convertible, would have been
entitled to receive had the exercise occurred as of the record date for such
dividend or distribution.

                  (e)      Liquidation; Dissolution. If the Company shall
dissolve, liquidate or wind up its affairs, the Holder shall have the right, but
not the obligation, to exercise this Warrant effective as of the date of such
dissolution, liquidation or winding up. If any such dissolution, liquidation or
winding up results in any cash distribution to the Holder in excess of the
aggregate Exercise Price for the shares of Series B Preferred Stock for which
this Warrant is exercised, then the Holder may, at its option, exercise this
Warrant without making payment of such aggregate Exercise Price and, in such
case, the Company shall, upon distribution to the Holder, consider such
aggregate Exercise Price to have been paid in full, and in making such
settlement to the Holder, shall deduct an amount equal to such aggregate
Exercise Price from the amount payable to the Holder.

                                      -5-

<PAGE>

                  (f)      Other Dilutive Events. If any event occurs as to
which the other provisions of this Section 7 are not strictly applicable but the
failure to make any adjustment would not fairly protect the purchase rights
represented by this Warrant in accordance with the essential intent and
principles hereof, then, in each such case, the Company shall appoint a firm of
independent public accountants of recognized national standing (which may be the
Company's regular auditors) which shall give their opinion upon the adjustment,
if any, on a basis consistent with the essential intent and principles
established in this Section 7, necessary to preserve, without dilution, the
purchase rights represented by this Warrant. Upon receipt of such opinion, the
Company shall promptly mail a copy thereof to the Holder and shall make the
adjustments described therein.

                  (g)      Certificates and Notices.

                           (i)      Adjustment Certificates. Upon any adjustment
of the Exercise Price and/or the number of shares of securities purchasable upon
exercise of this Warrant, a certificate signed by (A) the Company's President
and Chief Financial Officer, or (B) any independent firm of certified public
accounts of recognized national standing the Company selects at its own expense,
setting forth in reasonable detail the events requiring the adjustment and the
method by which such adjustment was calculated, shall be mailed to the Holder
and shall specify the adjusted Exercise Price and the number of shares of
securities purchasable upon exercise of the Warrant after giving effect to the
adjustment.

                           (ii)     Extraordinary Corporate Events. If the
Company, after the date hereof, proposes to effect (A) any transaction described
in Section 7(c) hereof, (B) a liquidation, dissolution or winding up of the
Company described in Section 7(f) hereof, (C) a sale of assets transaction
described in Section 7(a) hereof, or (D) any public offering of securities of
the Company or any payment of a dividend or distribution with respect to Series
B Preferred Stock or Common Stock of the Company, then, in each such case, the
Company shall mail to the Holder a notice describing such proposed action and
specifying the date on which the Company's books shall close, or a record shall
be taken, for determining the holders of stock entitled to participate in such
action, or the date on which such reclassification, liquidation, dissolution,
winding up or other action shall take place or commence, as the case may be, and
the date as of which it is expected that holders of stock of record shall be
entitled to receive securities and/or other property deliverable upon such
action, if any such date is to be fixed. Such notice shall be mailed to the
Holder at least thirty (30) days prior to the record date for such action in the
case of any action described in clause (A) or clause (C) above, and in the case
of any action described in clause (B) above, at least fifteen (15) days prior to
the date on which the action described is to take place and at least fifteen
(15) days prior to the record date for determining holders of Series B Preferred
Stock or Common Stock entitled to receive securities and/or other property in
connection with such action.

                  (h)      No Impairment. The Company shall not, by amendment of
the Articles of Incorporation or through any reorganization, recapitalization,
transfer of assets, consolidation, merger, dissolution, issue or sale of
securities or any other voluntary action, avoid or seek to avoid the observance
or performance of any of the terms to be observed or performed hereunder by the
Company, but shall at all times in good faith assist in the carrying out of all
the provisions of this Section 7 and in the taking of all such action as may be
necessary or appropriate in order to protect the rights of the Holder against
impairment.

                                       -6-

<PAGE>

                  (i)      Application. Except as otherwise provided herein, all
sections of this Section 7 are intended to operate independently of one another.
If an event occurs that requires the application of more than one section, all
applicable sections shall be given independent effect.

                  (j)      Authorized Shares. The Company covenants that during
the period the Warrant is outstanding, it shall reserve from its authorized and
unissued Series B Preferred Stock and Common Stock a sufficient number of shares
to provide for the issuance of Series B Preferred Stock upon the exercise of
this Warrant and issuance of Common Stock upon conversion of such Series B
Preferred Stock.

         8.       Exercise Price Adjustment. The number of shares of Common
Stock issuable upon conversion of the Warrant Shares and the terms for such
conversion, shall be subject to adjustment from time to time in the manner
governing the Company's Series B Preferred Stock in the Company's Certificate of
Incorporation. The provisions set forth for the Warrant Shares in the Company's
Certificate of Incorporation relating to the above adjustments, as of the date
of this Warrant, shall not be amended, modified or waived without the prior
written consent of the Holder, unless such amendment, modification or waiver is
in accordance with the Company's Certificate of Incorporation and applicable law
and affects the Holder in the same manner as it affects all other shareholders
of Series B Preferred Stock.

         9.       Notices. All notices permitted or required hereunder shall be
in writing and shall be delivered by hand, by overnight courier providing
regular nationwide service or by deposit in the United States mail, postage
prepaid, by registered or certified mail, return receipt requested, addressed to
the Company or the Holder, as the case may be, at the address of such party
below:

               (i)  if to the Company to:

                         Cytokinetics, Incorporated
                         Attn: Robert Blum, Vice President, Business Development
                         280 East Grand Avenue
                         South San Francisco, CA 94080

               (ii) if to the Holder to:

                         The Magnum Trust
                         c/o Peter E.F. Newbald
                         No. 1 Seaton Place
                         St. Helier, Jersey JE4 SYJ
                         Channel Islands

                   With a copy of any notice to Holder to:

                   Gregory Tolaram
                   Hamilton Capital Limited
                   101 Front Street
                   Mercury House
                   Hamilton HM 12, Bermuda

                                      -7-

<PAGE>

         Notices given by mail shall be deemed to be effective on the earlier of
the date shown on proof of receipt of such mail or, unless the recipient proves
that the notice was received later or not received, five (5) days after the date
of mailing thereof. Other notices shall be deemed given on the date of receipt.
The Company and any Holder may change the address specified above by written
notice to the other party hereto.

         10.      Miscellaneous. This Warrant may be amended and any term of
this Warrant may be waived only by a written instrument signed by the Company
and the Warrant holder. This Warrant shall be binding upon any successors or
assigns of the Company. This Warrant shall constitute a contract under the laws
of the State of California and for all purposes shall be construed in accordance
with and governed by the laws of said state applied without reference to
conflict of laws principles except to the extent that the Warrant Shares and
terms relating thereto are governed by Delaware law.

Dated: As of August 30, 1999

                                           CYTOKINETICS, INCORPORATED

                                           /s/ James Sabry
                                           ---------------------------------
                                           Name: JAMES SABRY
                                           Title: PRESIDENT AND CEO

                                      -8-

<PAGE>

                                    EXHIBIT A

                               NOTICE OF EXERCISE

TO: CYTOKINETICS, INCORPORATED

         (1)      The undersigned hereby elects to purchase _____ shares of
Series B Preferred Stock of Cytokinetics, Incorporated pursuant to the terms of
the attached Warrant, and tenders payment of the purchase price in full,
together with all applicable transfer taxes, if any.

         (2)      Please issue a certificate or certificates representing said
shares of Series B Preferred Stock in the name of the undersigned.

         (3)      The undersigned represents that the aforesaid shares of Series
B Preferred Stock are being acquired for the account of the undersigned for
investment and not with a view to, or for resale in connection with, the
distribution thereof and that the undersigned has no present intention of
distributing or reselling such shares.

(Date)

                                               _________________________________
                                               (Signature)

                                               _________________________________
                                               (Print Name)

<PAGE>

                                    EXHIBIT B

                              NOTICE OF CONVERSION

         To: ___________________

         (1)      The undersigned Warrant Holder hereby elects to exercise its
conversion rights under Section 2(b) of the Warrant dated as
of_______________________, 1999 between Cytokinetics, Incorporated and such
Holder (the "Warrant") and to acquire________________shares of stock of
Cytokinetics, Incorporated pursuant to such Section 2(b).

         (2)      In exercising its rights to convert the Warrant, the
undersigned hereby confirms and acknowledges the investment representations and
warranties made in Section 3(a) of the Warrant.

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

                                               _________________________________
                                               (name for issuance)

                                               _________________________________
                                               (address)

                                               _________________________________
                                               (address)

                                               WARRANT HOLDER:

                                               _________________________________
                                               (Warrant Holder signature)

                                               Date:____________________________

<PAGE>

                                    EXHIBIT C

                       INVESTMENT REPRESENTATION STATEMENT

         STOCKHOLDER       :     ___________________________

         COMPANY           :     Cytokinetics, Incorporated

         SECURITY          :     Series B Preferred Stock

         AMOUNT            :

         DATE              :

In connection with the purchase of the above-listed Securities, the undersigned
Stockholder represents to the Company the following:

                  (a)      Stockholder is aware of the Company's business
affairs and financial condition and has acquired sufficient information about
the Company to reach an informed and knowledgeable decision to acquire the
Securities. Stockholder is acquiring these Securities for investment for
Stockholder's own account only and not with a view to, or for resale in
connection with, any "distribution" thereof within the meaning of the Securities
Act of 1933, as amended (the "Securities Act").

                  (b)      Stockholder acknowledges and understands that the
Securities constitute "restricted securities" under the Securities Act and have
not been registered under the Securities Act in reliance upon a specific
exemption therefrom, which exemption depends upon, among other things, the bona
fide nature of Stockholder's investment intent as expressed herein. In this
connection, Stockholder understands that, in the view of the Securities and
Exchange Commission, the statutory basis for such exemption may be unavailable
if Stockholder's representation was predicated solely upon a present intention
to hold these Securities for the minimum capital gains period specified under
tax statutes, for a deferred sale, for or until an increase or decrease in the
market price of the Securities, or for a period of one year or any other fixed
period in the future. Stockholder further understands that the Securities must
be held indefinitely unless they are subsequently registered under the
Securities Act or an exemption from such registration is available. Stockholder
further acknowledges and understands that the Company is under no obligation to
register the Securities except as described in the Amended and Restated Investor
Rights Agreement of even date herewith. Stockholder understands that the
certificate evidencing the Securities will be imprinted with a legend which
prohibits the transfer of the Securities unless they are registered or such
registration is not required in the opinion of counsel satisfactory to the
Company, a legend prohibiting their transfer without the consent of the
Commissioner of Corporations of the State of California and any other legend
required under applicable state securities laws.

                  (c)      Stockholder is familiar with the provision of Rule
144, promulgated under the Securities Act, which, in substance, permit limited
public resale of "restricted securities" acquired,

<PAGE>

directly or indirectly from the issuer thereof, in a non-public offering subject
to the satisfaction of certain conditions.

                  The Securities may be resold in certain limited circumstances
subject to the provisions of Rule 144, which requires the resale to occur not
less than one year after the later of the date the Securities were sold by the
Company or the date the Securities were sold by an affiliate of the Company,
within the meaning of Rule 144; and, in the case of acquisition of the
Securities by an affiliate, or by a non-affiliate who subsequently holds the
Securities less than two years, the satisfaction of certain conditions of
Section 13 or 15(d) of the Securities Exchange Act of 1934, ninety (90) days
thereafter (or such longer period as any market stand-off agreement may require)
the Securities may be resold, subject to the satisfaction of certain of the
conditions specified by Rule 144, including: (1) the resale being made through a
broker in an unsolicited "broker's transaction" or in transactions directly with
a market maker (as said term is defined under the Securities Exchange Act of
1934); and, in the case of an affiliate, (2) the availability of certain public
information about the Company, (3) the amount of Securities being sold during
any three month period not exceeding the limitations specified in Rule 144, and
(4) the timely filing of a Form 144, if applicable.

                  (d)      Stockholder further understands that in the event all
of the applicable requirements of 144 are not satisfied, registration under the
Securities Act, compliance with Regulation A, or some other registration
exemption will be required; and that, notwithstanding the fact that Rule 144 is
not exclusive, the Staff of the Securities and Exchange Commission has expressed
its opinion that persons proposing to sell private placement securities other
than in a registered offering and otherwise than pursuant to Rule 144 will have
a substantial burden of proof in establishing that an exemption from
registration is available for such offers or sales, and that such persons and
their respective brokers who participate in such transactions do so at their own
risk. Stockholder understands that no assurances can be given that any such
other registration exemption will be available in such event.

                                             Signature of Stockholder;

                                             Date: ________________________

                                      -2-

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