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                                                                     Exhibit 4.3

                        INVESTOR EQUITYHOLDERS AGREEMENT

            THIS INVESTOR EQUITYHOLDERS AGREEMENT (this "AGREEMENT") is made as
of February 10, 2005 among Emergency Medical Services L.P., a Delaware limited
partnership (the "COMPANY"), Onex Partners LP, a Delaware limited partnership
("ONEX PARTNERS"), the equityholders listed on the signature pages of this
Agreement and such other equityholders of the Company as may, from time to time,
become parties to this Agreement in accordance with the provisions hereof.

            Upon consummation of the transactions contemplated by (a) the Stock
Purchase Agreement, dated as of December 6, 2004, by and among Laidlaw
International, Inc., Laidlaw Medical Holdings, Inc. and EMSC, Inc. with respect
to the acquisition of the common stock of EmCare Holdings Inc. ("EMCARE"), (b)
the Stock Purchase Agreement, dated as of December 6, 2004, by and among Laidlaw
International, Inc., Laidlaw Medical Holdings, Inc. and EMSC, Inc. with respect
to the acquisition of the common stock of American Medical Response, Inc.
("AMR") and of certain related transactions to be consummated concurrently
therewith (the "CLOSING"), Onex Partners and certain other equityholders will
own or may hereafter acquire certain Units (as defined below) and certain
options, and other rights to acquire Units from the Company, by exercise,
conversion, exchange or otherwise. The Company, the Onex Investors (as defined
below) and certain other Equityholders (as defined below) are parties to a
Registration Agreement (the "REGISTRATION AGREEMENT"), also dated as of the date
hereof.

            All of the Equityholders desire to enter into this Agreement for the
purpose of regulating certain aspects of the Equityholders' relationships with
one another and with the Company and in order to provide for the stability of
the Company.

            The parties, intending to be legally bound hereby, agree as follows:

                                    ARTICLE 1

                               Certain Definitions

            1.1 Certain Definitions. When used in this Agreement the following
terms shall have the respective meanings shown:

            "AFFILIATE" means, with respect to any Person, (a) any director or
executive officer of such Person, (b) any spouse, parent, sibling, descendant or
trust for the exclusive benefit of such Person or his or her spouse, parent,
sibling or descendant (or the spouse, parent, sibling or descendant of any
director or executive officer of such Person), and (c) any other Person that,
directly or indirectly, controls or is controlled by or is under common control
with such Person. For the purpose of this definition, (i) "control" (including
with correlative meanings, the terms "controlling," "controlled by" and "under
common control with"), as used with respect to any Person, means the possession,
directly or indirectly, of the power to direct or cause the direction

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of the management and policies of such Person, whether through the ownership of
voting securities, status as a general partner, or by contract or otherwise and
(ii) Onex Corporation shall be deemed to control any Person controlled by Gerald
W. Schwartz so long as Mr. Schwartz controls Onex Corporation.

            "APPROVED SALE" has the meaning set forth in Section 5.2(a).

            "BOARD" means the board of directors of the Company, provided, that
at any time the "Company" is a limited partnership, the "Board" shall mean the
board of directors of the general partner of the Company.

            "BUSINESS DAY" means any day which is neither a Saturday or Sunday
nor a legal holiday on which banks are authorized or required to be closed in
New York City.

            "CALL PRICE" means, as of any date, with respect to any Put/Call
Securities, a per Unit price equal to the quotient of (a) the excess of (i) the
product of 6.5 times EBITDA over (ii) the aggregate amount of the Consolidated
Indebtedness as of the end of the period for which EBITDA is calculated, divided
by (b) the aggregate number of Units outstanding at the time of the relevant
Put/Call Event. If the relevant Put/Call Event occurs prior to the completion of
one full fiscal quarter from the date of this Agreement, the Call Price shall be
the cash price per Unit paid by the Management Investor for the Put/Call
Securities.

            "CAUSE", with respect to a Management Investor, shall have the
meaning ascribed to it under the executed written employment agreement between
such Management Investor and the Company (or a subsidiary thereof) or, if there
is no such employment agreement with a Management Investor, it shall have the
meaning ascribed to it in the Company's Equity Option Plan as in effect on the
date hereof.

            "COMPANY" means Emergency Medical Services L.P., and any successor
thereto resulting from any merger, consolidation or other reorganization of or
including the Company.

            "CONSOLIDATED INDEBTEDNESS" means, as of any date, the aggregate
amount outstanding, on a consolidated basis, of (a) all obligations of the
Company or its subsidiaries for borrowed money, (b) all obligations of the
Company or its subsidiaries evidenced by bonds, debentures, notes or other
similar instruments or upon which interest charges are customarily paid, (c) all
obligations of the Company or its subsidiaries for the deferred purchase price
of property or services, except current accounts payable arising in the ordinary
course of business and not overdue beyond such period as is commercially
reasonable for the Company or its subsidiaries' business, (d) all obligations of
the Company or its subsidiaries under conditional sale or other title retention
agreements relating to property purchased by such Person and all capitalized
lease obligations, (e) all payment obligations of the Company or its
subsidiaries on or for currency protection agreements, (f) all obligations of
the Company or its subsidiaries as an account party under any letter of credit
(excluding those supporting trade payables), (g) all obligations of any third
party secured by property or assets of the Company or its subsidiaries

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(regardless of whether or not such Person is liable for repayment of such
obligations) and (h) all guarantees of the Company or its subsidiaries.

            "EBITDA" means the consolidated net income of the Company and its
subsidiaries, adjusted by adding thereto, to the extent deducted in determining
such consolidated net income, interest, taxes, depreciation and amortization for
the four consecutive fiscal quarters immediately preceding the relevant Put/Call
Event, as calculated in accordance with generally accepted accounting principles
in the United States consistently applied, based on the Company's consolidated
financial statements for the applicable period. If fewer than four full fiscal
quarters have elapsed from the date of this Agreement through the date of the
relevant Put/Call Event, EBITDA shall be determined by reference to the results
of such full fiscal quarters, divided by the number of such full fiscal
quarters, and multiplied by four. The Board may make such adjustments to EBITDA
as it determines in good faith are appropriate to reflect non-recurring or
unusual items.

            "EQUITYHOLDER" means any holder of Units that is or becomes a party
to this Agreement.

            "EQUITYHOLDER REPRESENTATIVE" has the meaning set forth in Section
4.3(a).

            "MAJORITY ONEX INVESTORS" means Onex Investors holding, in the
aggregate, a majority of the Units held by all Onex Investors.

            "MANAGEMENT INVESTOR" means any of William A. Sanger, Don S. Harvey,
Randel G. Owen and Todd Zimmerman, and any other individual employed by the
Company or any subsidiary of the Company at the time he or she becomes a party
to this Agreement and is identified as a "Management Investor" on the signature
pages of this Agreement, in each case for so long as such individual is employed
by the Company or any subsidiary of the Company.

            "ONEX CORPORATION" means Onex Corporation, an Ontario corporation.

            "ONEX INVESTOR" means Onex Partners, Onex Corporation or any
Affiliate of Onex Partners or Onex Corporation that is a holder of Units or
other equity interests of the Company.

            "OTHER INVESTOR" means any holder of Units that is or becomes a
party to this Agreement other than (a) an Onex Investor and (b) the transferees
of the Onex Investors that acquire all of the Units held by the Onex Investors
as of the date hereof.

            "PERSON" means an individual, a partnership, a joint venture, a
corporation, a limited liability company, a trust, an unincorporated
organization or a government or any department or agency thereof.

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            "PUBLIC OFFERING" means a public offering and sale of equity
interests of the Company pursuant to an effective registration statement under
the Securities Act.

            "PUBLIC SALE" means any sale of Units to the public pursuant to an
offering registered under the Securities Act or to the public through a broker
or dealer or to a market maker pursuant to the provisions of Rule 144 (or any
similar provision then in force) adopted under the Securities Act.

            "PUT/CALL EVENT" has the meaning set forth in Section 5.3(a).

            "PUT PRICE" means, as of any date, with respect to any Put/Call
Securities, a per Unit price equal to the quotient of (a) the excess of (i) the
product of 4.5 times EBITDA, over (ii) the aggregate amount of the Consolidated
Indebtedness as of the end of the period for which EBITDA is calculated, divided
by (b) the aggregate number of Units outstanding at the time of the relevant
Put/Call Event. If the relevant Put/Call Event occurs prior to the completion of
one full fiscal quarter from the date of this Agreement, the Put Price shall be
the cash price per Unit paid by the Management Investor for the Put/Call
Securities.

            "PUT/CALL SECURITIES" means all of the Units owned by a Management
Investor and any transferee for whom the Management Investor serves as the
Equityholder Representative.

            "QUALIFIED PUBLIC OFFERING" means the sale in one or more
underwritten public offerings registered under the Securities Act of at least
20% of the equity interests in the Company outstanding immediately after giving
effect to the most recent such offering.

            "SALE OF THE COMPANY" means any transaction pursuant to which
Person(s) other than the Company's existing equityholders as of the date hereof
and their respective Affiliates acquire (a) equity interests of the Company
possessing the voting power under normal circumstances to elect a majority of
the Board (whether by merger, consolidation, recapitalization, reorganization or
sale or transfer of the Company's equity interests or otherwise) or (b) all or
substantially all of the Company's assets (determined on a consolidated basis).

            "SECURITIES ACT" means the Securities Act of 1933, as amended from
time to time.

            "UNITS" means (a) the units representing the Company's limited
partnership interests purchased, issued to or otherwise acquired by any
Equityholder (and includes Class A Units and Class B Units), including Units
acquired upon the exercise of any warrant or option, and (b) any equity
securities issued or issuable, directly or indirectly, with respect to the
securities referred to in clause (a) by way of dividend or unit split, exchange
or conversion, or in connection with a combination of units, shares,
recapitalization, merger, consolidation or other reorganization. As to any
particular equity interests constituting Units, such units will continue to be
Units subject to this Agreement in the hands of any holder of such Units (other
than purchasers pursuant to a Public Sale).

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                                    ARTICLE 2

                        Board of Directors of the Company

            2.1 Board of Directors. (a) Each of the Equityholders will vote all
of its Units, and the Company will take all necessary or desirable action within
its control, in order to cause the election to the Board of such individuals as
may be designated from time to time by the Majority Onex Investors.

            (b) The provisions of this Article 2 will terminate automatically
upon the earlier to occur of (i) an Approved Sale or (ii) a Qualified Public
Offering.

                                    ARTICLE 3

                   Covenants of the Company and Other Matters

            3.1 Financial Information. So long as an Equityholder owns any Unit,
the Company shall furnish or otherwise make available to such Equityholder the
following:

            (a) as promptly as practicable, and in any event within 90 days
after the end of each fiscal year of the Company, copies of the audited annual
consolidated financial statements of the Company and its subsidiaries, including
a consolidated balance sheet of the Company and its subsidiaries as at the end
of such fiscal year, consolidated statements of income and of cash flow of the
Company and its subsidiaries for such fiscal year and the related notes thereto,
and stating in comparative form the figures as of the end of and for the
previous fiscal year, accompanied by an audit report thereon by a firm of
independent certified public accountants of national recognition, and

            (b) as promptly as practicable, and in any event within 45 days
after the end of each fiscal quarter of the Company, copies of the unaudited
quarterly consolidated financial statements of the Company, including a
consolidated balance sheet of the Company and its subsidiaries as at the end of
such fiscal quarter, and consolidated statements of income and of cash flow of
the Company and its subsidiaries for such fiscal quarter and year to date
period, and stating in comparative form the figures as of the end of and for the
corresponding fiscal quarter and year to date period in the previous fiscal
year; provided, that such statements need not cover periods prior to the date
hereof.

            The Board may require that Other Investors execute a confidentiality
agreement acceptable to the Board as a condition to the receipt of the financial
information set forth in this Sections 3.1, but such confidentiality agreement
shall not apply to any financial information made publicly available by the
Company in connection with or following a Public Offering.

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            3.2 Multiple Voting Stock upon IPO. The Equityholders hereby agree
to approve and to raise no objection to the implementation, at the election of
the Majority Onex Investors in connection with an initial Public Offering, of a
multiple vote stock to be exchanged for the Units that are held by the
Equityholders. In the event that such multiple vote stock is issued, the
Equityholders agree to enter into a voting agreement which provides that each
Equityholder, so long as such Equityholder holds Company common stock exchanged
for Units, will vote for the election to the Board of individuals designated
from time to time by the Majority Onex Investors. Such voting arrangement will
terminate at such time as the Onex Investors cease to own in the aggregate at
least 10% of the Company's equity securities held by them immediately after
giving effect to the initial Public Offering.

                                    ARTICLE 4

                        Restrictions on Transfer of Units

            4.1 Transfer of Equityholder Units. No Other Investor shall sell,
transfer, assign, pledge, exchange or otherwise dispose of (a "TRANSFER") any
interest in Units except pursuant to the provisions of this Article 4, Article 5
or pursuant to a Public Sale.

            4.2 First Offer Right.

            (a) At any time after the fifth anniversary of the date of this
Agreement and prior to a Qualified Public Offering, any Other Investor (the
"TRANSFERRING EQUITYHOLDER") may Transfer Units pursuant to a bona fide offer
from a Person other than an Affiliate of such Other Investor by complying with
this Section 4.2. In order to do so, the Transferring Equityholder must deliver
a notice (the "OFFER NOTICE") to the other Equityholders and to the Company,
disclosing the proposed number of Units (the "SUBJECT UNITS") to be transferred,
the identity of the proposed purchasers, and, in reasonable detail, the proposed
terms and conditions of the Transfer, which must include payment of the purchase
price in cash at the closing of the Transfer. Then, each of the Equityholders
other than the Transferring Equityholder (collectively the "FIRST OFFER
EQUITYHOLDERS") may elect to purchase its First Offer Percentage of the Units
specified in the Offer Notice at the price per Unit in cash and on the other
terms specified therein by delivering notice of such election to the
Transferring Equityholder within 30 days after the delivery of the Offer Notice;
if less than all of the First Offer Equityholders elect to make such purchase,
the remaining Subject Units shall be reoffered to those First Offer
Equityholders who have elected to make such purchase under procedures specified
by the Company until either an election to purchase all of the Subject Units has
been made or no First Offer Equityholder is willing to increase the number of
Subject Units that it is electing to purchase. If the First Offer Equityholders
have not elected to purchase all of the Subject Units within 45 days after
delivery of the Offer Notice, the Company may elect to purchase all (but not
less than all) of the Subject Units that the First Offer Equityholders did not
elect to purchase at the price per unit in cash and on the other terms specified
in the Offer Notice by delivering notice of such election to the Transferring
Equityholder within 60 days after delivery of the Offer Notice. If the Company
and/or the First Offer Equityholders have elected to purchase all (but not less
than all) of the Subject Units from the Transferring Equityholder, the transfer
of such Units pursuant to such elections will be consummated at a time and place
specified by the Company within 90 days after delivery of the Offer Notice. If
(and only if) the Company and the First Offer Equityholders have not elected to
purchase all of the Subject Units within 60 days after delivery of the Offer
Notice, the elections of the Company and the First Offer Equityholders to
purchase less than all of the Subject Units shall be ineffective and the
Transferring Equityholder may, not less than 90 days or more than 120 days after
delivery of the Offer Notice, transfer all (but not less than all) of the

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Subject Units to the proposed purchasers set forth in the Offer Notice at the
same price per Unit in cash and on the same other terms offered to the Company
and the First Offer Equityholders in the Offer Notice; provided, that prior to
such Transfer, such transferees shall have agreed in writing to be bound by the
provisions of this Agreement. If the Subject Units are not so transferred within
such period, they will be subject to the provisions of this Section 4.2(a) with
respect to subsequent transfer and the Transferring Equityholder will not be
entitled to deliver another Offer Notice for 90 days after the Subject Units
again become subject to this Section 4.2(a).

            (b) If the Board determines in good faith that the acquisition of
Units by a proposed purchaser identified in an Offer Notice could have an
adverse effect on the Company for competitive or regulatory reasons, the Company
shall deliver notice of that determination to the Equityholders within 20 days
after delivery of the Offer Notice and such Offer Notice shall be void and of no
effect. The Transferring Equityholder shall provide the Board with such
information as the Board may reasonably request in order to make that
determination and the 20-day period referred to in the preceding sentence shall
be tolled during any period in which such information has been requested and not
supplied.

            (c) The Equityholders may transfer any of their respective rights to
purchase the Subject Units under Section 4.2(a) to any of their respective
Affiliates; provided, that prior to such transfer, such Affiliate shall have
agreed in writing to become a party to this Agreement.

            (d) A First Offer Equityholder's "FIRST OFFER PERCENTAGE" is the
quotient obtained by dividing the number of Units held by such First Offer
Equityholder by the number of Units held by all First Offer Equityholders.

            4.3 Permitted Transfers.

            (a) The restrictions contained in this Article 4 shall not apply
with respect to (i) any Transfer of Units by any Equityholder to or among its
Affiliates or (ii) any Transfer of Units by any Equityholder to any other
Equityholder; provided, that the restrictions contained in this Article 4 shall
continue to be applicable to the Units after any such Transfer and provided
further that the transferees of such Units shall have agreed in writing to
become parties to this Agreement. Any Management Investor transferring Units
pursuant to this Section 4.3(a)(i) shall remain the "EQUITYHOLDER
REPRESENTATIVE" with respect to all such transferred Units and shall be
responsible for all consents, notices and other communication between the
Company and the other Equityholders, on the one hand, and the transferee(s) of
such Units, on the other hand, as

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well as receipt of the Call Price, if applicable. Without limiting the
foregoing, (i) only the Equityholder Representative shall give or receive any
Offer Notice, Put Notice or Call Notice or have the right to elect to purchase
Units under Section 4.2(a) or to sell Units under Section 5.3(a), (ii) the
number of Units held by the Equityholder Representative as a First Offer
Equityholder shall be deemed to include the Units held by his transferee(s), and
(iii) the Units held by the Equityholder Representative's transferees shall be
deemed to be Put/Call Securities of the Equityholder Representative and all
references to "Management Investor" in Section 5.3 shall be deemed to include
such transferees.

            (b) Notwithstanding the provisions of Section 4.2, from the date the
Company completes a Qualified Public Offering, an Other Investor may sell
Pre-QPO Units only pursuant to Public Sale, and limited to a percentage of the
Other Investor's Pre-QPO Units equal, at the date of any Public Sale, to:

                  (i) the greater of

                  (a) 50% of the Other Investor's Pre-QPO Units, such Public
Sale rights accruing in cumulative installments of 12.5% of the Other Investor's
Pre-QPO Units in each 12-month per commencing with (and including any Pre-QPO
Units sold in) the Qualified Public Offering, and

                        (b) the percentage of Onex Partner's Pre-QPO Units old
      by Onex Partners, plus

                  (ii) upon the exercise of an option granted under a Company
      plan for employees, a number of Pre-QPO Units having an aggregate sale
      price equal to the income taxes payable by the Other Investor as a result
      of such exercise, provided, that the Public Sale occurs within five
      Business Days of the exercise, minus

                  (iii) the Pre-QPO Units previously sold by the Other Investor,
      whether pursuant to this Section 4.3(b) or otherwise.

Any sale pursuant to this Section 4.3(b) shall be subject to the provisions of
Section 3 of the Registration Agreement.

As used herein, the term "PRE-QPO UNITS", as to any Person, means the Units held
by that Person immediately prior to the consummation of a Qualified Public
Offering, and including any Units issued upon the exercise of any warrant or
option held by that Person immediately prior to the consummation of a Qualified
Public Offering.

            (c) The provisions of this Article 4 shall terminate automatically
upon the earlier to occur of (i) an Approved Sale and (ii) the fifth anniversary
of a Qualified Public Offering.

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            (d) In the case of any Transfer pursuant to Section 4.3(a)(i), a
transferee may at any time, and shall forthwith in the event that such
transferee ceases to be an Affiliate of the transferor, transfer back to such
transferor all of the Units held by it.

                                    ARTICLE 5

                    Tag-Along, Drag-Along and Put/Call Rights

            5.1 Tag-Along Right.

            (a) At least 30 days prior to any Transfer of Units by any Onex
Investor (the "INITIATING EQUITYHOLDER"), such Initiating Equityholder shall
deliver a written notice (the "SALE NOTICE") to each other Equityholder
(including any other Onex Investor), specifying in reasonable detail the
identity of the prospective transferee(s), the number of Units to be
transferred, the price per Unit to be paid for such Units, and the other terms
and conditions of the Transfer. Each of such other Equityholders may elect to
participate in the contemplated Transfer at the same price per share and on the
same terms by delivering written notice to the Initiating Equityholder within 15
days after delivery of the Sale Notice (each such electing Equityholder is a
"PARTICIPATING EQUITYHOLDER"). Each Participating Equityholder will be entitled
and obligated to sell in the contemplated Transfer, at the price per Units and
on the same terms, a number of Units equal to such Participating Equityholder's
Tag-Along Percentage of the number of Units proposed to be transferred by the
Initiating Equityholder and the number of Units to be transferred by the
Initiating Equityholder in such contemplated Transfer shall be reduced by the
number of Units to be transferred by the Participating Equityholders (unless the
Initiating Equityholder purchases such Units directly from the Participating
Equityholders pursuant to Section 5.1(b)), simultaneously with and conditioned
upon the closing of the sale by the Initiating Equityholder. The Initiating
Equityholder may abandon the contemplated Transfer at any time prior to its
closing without any liability or obligation under this Section 5.1. A
Participating Equityholder's "TAG-ALONG PERCENTAGE" is the quotient obtained by
dividing the number of Units owned by such Participating Equityholder by the sum
of the aggregate number of Units owned by the Equityholders (including the
Initiating Equityholder) and, without duplication, all other holders having
co-sale rights with respect to such Transfer.

            (b) The Initiating Equityholder shall effect the participation of
the Participating Equityholders in the contemplated Transfer by either (i)
obtaining the agreement of the prospective transferee(s) to purchase from the
Participating Equityholders the Units which the Participating Equityholders are
entitled to sell to such prospective transferee(s) pursuant to Section 5.1(a) or
(ii) purchasing the number of Units from the Participating Equityholders which
the Participating Equityholders would have been entitled to sell to the
transferee(s) pursuant to Section 5.1(a) at the same price per Unit and on the
same terms and conditions at which such Participating Equityholders are entitled
otherwise to sell such Units to the transferee(s) pursuant to Section 5.1(c), in
either case simultaneously with and conditioned upon the closing of the proposed
Transfer.

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            (c) The Participating Equityholders will use their best efforts to
cooperate in the proposed Transfer and will take all necessary and desirable
actions in connection with the consummation of the proposed Transfer as are
reasonably requested by the Initiating Equityholder, including, but not limited
to, entry into agreements and provision of representations, warranties and
indemnification; provided, that no Participating Equityholder shall be required
to enter into substantively different agreements or provide substantively
different representations and warranties or indemnification than the Initiating
Equityholder and each Participating Equityholder's obligations thereunder shall
be several and limited to the proceeds received by such Equityholder in
connection with such proposed Transfer.

            (d) Prior to transferring its Units pursuant to this Section 5.1,
the Initiating Equityholder shall cause the prospective transferee to agree in
writing to become a party to this Agreement.

            (e) The provisions of this Section 5.1 shall not apply to any Public
Sale or Public Offering, to any Transfer in connection with a Sale of the
Company or to any Transfer to an Onex Investor or an Affiliate of an Onex
Investor; provided, that any Affiliate of an Onex Investor to which Units are
transferred must have agreed in writing to become a party to this Agreement.

            5.2 Drag-Along Right.

            (a) Subject to Section 5.2(b), if the Majority Onex Investors
approve a Sale of the Company (the "APPROVED SALE"), the Equityholders will
consent to and raise no objections to the Approved Sale and (i) if the Approved
Sale is structured as a sale of Units, the Equityholders will sell all of their
Units and rights to acquire Units on the terms and conditions approved by the
Majority Onex Investors, (ii) if the Approved Sale is structured as a merger,
consolidation or other reorganization, the Equityholders will vote in favor
thereof and will not exercise any dissenters' rights of appraisal they may have
under Delaware law, and (iii) if the Approved Sale is structured as a sale of
all or substantially all of the Company's consolidated assets, the Equityholders
will vote in favor thereof. The Equityholders will use their best efforts to
cooperate in the Approved Sale and will take all necessary and desirable actions
in connection with the consummation of the Approved Sale as are reasonably
requested by the Majority Onex Investors, including, but not limited to, entry
into agreements and provision of representations, warranties and
indemnification, provided, that no Equityholder shall be required to enter into
substantively different agreements or provide substantively different
representations and warranties or indemnification than any other Equityholder
and each Equityholder's obligations thereunder shall be several and limited to
the proceeds received by such Equityholder in connection with such Approved
Sale.

            (b) The obligations of the Equityholders with respect to the
Approved Sale are subject to the satisfaction of the following conditions: (i)
upon the consummation of the Approved Sale, all of the Equityholders will
receive the same form and per Unit amount of consideration for their Units as
all other Equityholders, or if any Equityholders are given an

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option as to the form and amount of consideration to be received, all
Equityholders must be given the same option (except that the Approved Sale may
provide for payment in securities to all Equityholders that are accredited
investors within the meaning of Regulation D under the Securities Act and in
cash to Equityholders that are not accredited investors or may provide
Equityholders that are accredited investors with the option to receive
securities or cash while Equityholders that are not accredited investors receive
cash); and (ii) if the Approved Sale includes a sale to a Person that is an Onex
Investor or an Affiliate of an Onex Investor, the holders of a majority of the
Units held by the Other Investors may request that an appraisal of the fair
market value of the securities to be sold and/or received (based on the fair
market value of all of the Company's outstanding equity interests, without
regard to any control premium or liquidity or minority discount) by the Other
Investors in connection with such Approved Sale be made by an investment banking
firm of national recognition mutually agreeable to such parties, and it shall be
a condition to the consummation of such Approved Sale to an Onex Investor or an
Affiliate of an Onex Investor that such Person pay as consideration to the Other
Investors the fair market value as determined pursuant to such appraisal (if
such appraisal results in a valuation greater than the valuation of the
consideration proposed to be delivered in connection with such Approved Sale,
the Company shall pay the costs of such appraisal, otherwise the requesting
Equityholders shall pay such costs).

            (c) If the proposed Approved Sale involves the receipt by
Equityholders of securities for which Section 4(2) of the Securities Act of 1933
or Rule 506 (or any similar rule then in effect) promulgated by the Securities
and Exchange Commission may be available with respect to such negotiation or
transaction (including a merger, consolidation or other reorganization), the
Equityholders will, at the request of the Majority Onex Investors, and to the
extent required to comply with Regulation D, appoint a purchaser representative
(as such term is defined in Rule 501) reasonably acceptable to the Majority Onex
Investor. If any Equityholder appoints the purchaser representative designated
by the Majority Onex Investors, the Company will pay the fees of such purchaser
representative, but if any Equityholder declines to appoint the purchaser
representative designated by the Majority Onex Investors, such holder will
appoint another purchaser representative (reasonably acceptable to the Majority
Onex Investors), and such holder will be responsible for the fees of the
purchaser representative so appointed.

            (d) If in connection with an Approved Sale, an Onex Investor (the
"ROLLOVER INVESTOR") intends to invest in securities (the "SUCCESSOR
SECURITIES") of the acquiring, successor or post-acquisition entity pursuant to
an agreement or understanding reached in connection with the Approved Sale
(whether through a direct purchase, rollover or otherwise, the "ROLLOVER
INVESTMENT"), the Rollover Investor shall deliver written notice (the "ROLLOVER
NOTICE") to each of the Other Investors no later than 15 days prior to the
consummation of such Rollover Investment, describing in reasonable detail the
number and type of Successor Securities subject to such proposed Rollover
Investment, the price per security and the other terms and conditions of such
Rollover Investment. Each Other Investor may elect to participate in such
Rollover Investment by delivering written notice to the Rollover Investor within
ten days after the delivery of the Rollover Notice (each such electing Other
Investor, a "ROLLOVER EQUITYHOLDER"). If the Rollover Investor actually makes
the Rollover Investment in Successor Securities, each Rollover

                                       11
<PAGE>

Equityholder shall be entitled to invest in a number of Successor Securities
equal to such Rollover Equityholder's Rollover Percentage of the Successor
Securities subject to the Rollover Investment, at the same price per security
and on the same terms, as described in the Rollover Notice. A Rollover
Equityholder's "ROLLOVER PERCENTAGE" is the quotient obtained by dividing the
number of shares of Units owned by such Rollover Equityholder by the sum of the
aggregate number of Units owned by the Equityholders (including the Onex
Investors). The Rollover Investor shall effect the participation of the Rollover
Equityholders in the Proposed Rollover Investment by either (i) obtaining the
agreement of the prospective issuer of the Successor Securities to permit the
Rollover Equityholders to directly invest in Successor Securities or (ii) by
requiring each Rollover Equityholders to make his/her/its investment through an
investment vehicle controlled by an Onex Investor or an Affiliate of an Onex
Investor. Notwithstanding the foregoing, a Rollover Equityholder shall not be
entitled to participate in a Rollover Investment (a) if such Rollover
Equityholder is not an accredited investor within the meaning of Regulation D
under the Securities Act or (b) if participation by such Rollover Equityholder
would make unavailable any exemption from registration under the Securities Act
or the Investment Company Act of 1940, as amended, which has been relied on by
the acquiring, successor or post-acquisition entity.

            5.3 Put/Call Rights on Certain Events.

            (a) If, prior to a Qualified Public Offering, a Management Investor
dies or suffers a permanent disability, or is terminated by the Company or a
subsidiary of the Company without Cause (the "PUT/CALL EVENT"), then such
Management Investor (or, in the case of death or permanent disability, such
Management Investor's executor, personal representative or legal representative)
shall have the right to require the Company to purchase (the "PUT OPTION"), by
delivery of a written notice (the "PUT NOTICE") to the Company within 30 days
after the date of the Put/Call Event (the "PUT PERIOD"), and the Company shall
be required to purchase, all of the Put/Call Securities at a price per Unit
equal to the Put Price as of the date of the Put/Call Event. If the Put Option
is not exercised within the Put Period, then the Company shall have the right to
require the Management Investor to sell (the "CALL OPTION"), by delivery of a
written notice (the "CALL NOTICE") to the Management Investor (or, in the case
of death or permanent disability, such Management Investor's executor, personal
representative or legal representative) within 60 days after the date of the
Put/Call Event (or, if later, the fifth Business Day after all options to
purchase Units held by the Management Investor have been exercised or expired by
their terms) (the "CALL PERIOD"), and the Management Investor shall be required
to sell, all of the Put/Call Securities at a price Per Unit equal to the Call
Price as of the date of the Put/Call Event. As used herein, "PERMANENT
DISABILITY" of a Management Investor means a physical or mental medical
condition that renders such Management Investor incapable of full time
employment and which is reasonably expected to continue to have such effect for
more than one year. Any Management Investor who seeks to exercise the Put Option
by reason of a permanent disability shall (i) authorize and direct his or her
physicians and other health care professionals to discuss his or her medical
condition with representatives of the Company (waiving any applicable privilege)
and (ii) submit to examination by physicians designated by the Company.

                                       12
<PAGE>

            (b) If, prior to a Qualified Public Offering, a Management Investor
is terminated by the Company or a subsidiary of the Company for Cause, then the
Company shall have the right to require the Management Investor to sell, by
delivery of a written notice (the "CAUSE CALL NOTICE") to the Management
Investor within 60 days after the date of termination (or, if later, the fifth
Business Day after all options to purchase Units held by the Management Investor
have been exercised or expired by their terms) (the "CAUSE CALL PERIOD"), and
the Management Investor shall be required to sell, all of the Put/Call
Securities at a price per Unit equal to the Put Price as of the date of
termination.

            (c) The closing of any purchase of Put/Call Securities by the
Company pursuant to this Section 5.3 shall take place at the principal office of
the Company within 15 days after the expiration of the relevant Put Period, Call
Period or Cause Call Period as the Company shall specify to such Management
Investor (or, in the case of death or permanent disability, such Management
Investor's executor, personal representative or legal representative) in writing
(or such later date designated by the Company as may be necessary to determine
the Put Price or Call Price or confirm the existence of permanent disability).
At such closing, such Management Investor (or, in the case of death or permanent
disability, such Management Investor's executor, personal representative or
legal representative) shall deliver to the Company certificates and/or other
instruments representing, together with stock or other appropriate powers duly
endorsed with respect to, the Put/Call Securities, free and clear of all liens,
encumbrances or other restrictions (other than pursuant to securities laws or
this Agreement), against payment by the Company of the purchase price for the
Put/Call Securities in cash (by delivery of a certified check payable to such
Management Investor (or, in the case of death, such Management Investor's
estate)). Notwithstanding the foregoing, if the payment of all or any portion of
the purchase price is not permitted to be made at the closing by the terms any
credit agreement(s) relating to the Company's senior debt (collectively, the
"CREDIT AGREEMENT"), or the payment would cause a Default or an Event of Default
(as such terms are defined in any Credit Agreement), then that portion of the
purchase price shall instead become a subordinated obligation of the Company (a
"SUBORDINATE OBLIGATION"); the Subordinated Obligation shall not be payable
during the continuance of a Default or an Event of Default (as defined in any
Credit Agreement) or if such payment would not otherwise be permitted by any
Credit Agreement or would result in a Default or an Event of Default (as defined
under any Credit Agreement). The Subordinate Obligation shall be payable on the
earlier to occur of (i) one day after the closing date of a complete refinancing
of the Company's senior debt and (ii) receipt by the Company of the written
approval of its senior lenders to pay the principal and interest on the
obligation in full. The Subordinate Obligation shall accrue interest at the
weighted average rate applicable from time to time on the Company's senior debt.
The Company shall pre-pay the amount of any Subordinate Obligation, together
with accrued and unpaid interest, as and when it is permitted to do so without
Default (as defined) or creating an Event of Default (as defined) under any
Credit Agreement, provided, that if there is more than one Subordinate
Obligation outstanding, the Company shall make pre-payments on each Subordinate
Obligation in the proportion that the outstanding amount thereof (including
accrued and unpaid interest) bears to the aggregate outstanding Subordinate
Obligations (including accrued and unpaid interest).

                                       13
<PAGE>

            (d) If and to the extent a Management Investor (or, in the case of
death or permanent disability, a Management Investor 's executor, personal
representative or legal representative) does not deliver a Put Notice within the
Put Period or if the purchase of all Put/Call Securities does not occur at the
scheduled closing date through the fault of such Management Investor (or his
executor, personal representative or legal representative), then such Management
Investor 's Put Option shall terminate. If and to the extent the Company does
not deliver a Call Notice or a Cause Call Notice within the Call Period or the
Cause Call Period, as applicable, or if the purchase of all Put/Call Securities
does not occur at the scheduled closing date through the fault of the Company,
then the Company's Call Option, or option to purchase upon termination for
Cause, shall terminate.

            5.4 Termination. The provisions of this Article 5 shall terminate
automatically upon the earlier to occur of (a) an Approved Sale and (b) a
Qualified Public Offering.

                                    ARTICLE 6

                                Preemptive Rights

            6.1 Grant of Preemptive Right. Subject to Section 6.6, if the
Company, EmCare or AMR authorizes the issuance or sale of (a) any Units, (b)
shares of common stock, no par value per Share, of EmCare ("EMCARE SHARES"), (c)
shares of common stock, $0.01 par value per share, of AMR ("AMR SHARES" and
together with EmCare Shares, "SUBSIDIARY SHARES") or (d) securities convertible
into or exercisable for Units or Subsidiary Shares (together the "UNITS
EQUIVALENTS" and collectively with Units and Subsidiary Shares, the
"PARTICIPATION SECURITIES") to any Onex Investor or Affiliate of an Onex
Investor (other than the Company or any subsidiary of the Company), the Company,
EmCare or AMR (as the case may be, the "PARTICIPATION SECURITIES OFFEROR")
shall, on the terms and conditions of this Article 6, offer to each of the Other
Investors the right to purchase or subscribe for up to an aggregate number of
Participation Securities equal to the product of (i) the total number of
Participation Securities to be issued or sold by the Participation Securities
Offeror and (ii) a fraction, the numerator of which is the aggregate number of
Units held by such Other Investor, and the denominator of which is the aggregate
number of Units outstanding, in each case, determined as of the date of the
Preemptive Notice. For the purpose of this Article 6, "EQUITYHOLDER
PARTICIPATION SECURITIES" means, with respect to any Other Investor in
connection with any proposed issuance or sale of Participation Securities by the
Participation Securities Offeror, that number of Participation Securities as to
which such Other Investor is entitled to exercise preemptive rights hereunder,
calculated under the immediately preceding sentence. However, the Participation
Securities Offeror may elect not to extend preemptive rights to any Other
Investor that is not an "accredited investor" within the meaning of Regulation D
under the Securities Act or whose participation in the offering would, in the
reasonable judgment of the Participation Securities Offeror, require
registration or qualification under any federal, state or foreign securities law
and

                                       14
<PAGE>

if it does so the Persons so excluded shall not be Other Investors for any
purpose under this Article 6.

            6.2 Delivery of Preemptive Notice by Participation Securities
Offeror. If the Participation Securities Offeror proposes to issue or sell any
Participation Securities in a transaction giving rise to the preemptive rights
provided for in this Article 6, subject to Section 6.4, the Participation
Securities Offeror shall send a written notice (the "PREEMPTIVE NOTICE") to each
Other Investor at least 10 Business Days before the proposed date of such
issuance or sale, setting forth (a) the type and, if not Units or Subsidiary
Shares, the terms and conditions of the Participation Securities, (b) the number
of Participation Securities that the Participation Securities Offeror proposes
to sell or issue, (c) the price (before any commission or discount) at which
such Participation Securities are proposed to be issued or sold (or, in the case
of an offering in which the price is not known at the time the Preemptive Notice
is given, the method of determining such price and an estimate thereof), (d) the
other material terms of the transaction, and (e) the aggregate number of
Equityholder Participation Securities which may be purchased by such Other
Investor (determined under Section 6.1).

            6.3 Delivery of Exercise Notice; Waiver of Preemptive Right. At any
time within the ten Business Days following the date the Participation
Securities Offeror delivers the Preemptive Notice, an Other Investor may
exercise the preemptive rights provided under this Article 6 by delivering
notice to the Participation Securities Offeror (an "EXERCISE NOTICE") exercising
such Other Investor's preemptive rights as to all, but not less than all, of its
Equityholder Participation Securities. If any Other Investor does not deliver a
timely Exercise Notice, such Other Investor shall be deemed to have irrevocably
waived the preemptive rights provided by this Article 6 with respect to all
Participation Securities that are the subject of the Preemptive Notice, and the
Participation Securities Offeror shall be permitted to issue such Other
Investor's Equityholder Participation Securities free from the preemptive rights
provided under this Article 6.

            6.4 Terms of Issuance of Sale of Participation Securities.

            (a) Subject to Section 6.4(b), (c) and (d) below, the purchase of,
or subscription for Participation Securities by the Other Investors who exercise
preemptive rights under this Article 6, shall be at the same price and on the
same terms and conditions, including the date of sale or issuance, as are
applicable to the proposed issuance or sale by the Participation Securities
Offeror of the Participation Securities to any Onex Investor or Affiliate of an
Onex Investor.

            (b) If the Participation Securities Offeror determines in good faith
that the delay occasioned by complying with the procedures contemplated by this
Article 6 would be prejudicial to the Participation Securities Offeror or its
financial condition or business and operations, then the Participation
Securities Offeror may before delivering the Preemptive Notice or after
delivering the Preemptive Notice (but in such case before observing the time
periods and other procedures set forth in this Article 6), (i) issue or sell all
or any part of the Participation

                                       15
<PAGE>

Securities to any Onex Investor or Affiliate of an Onex Investor without issuing
or selling all or any part of the Equityholder Participation Securities of some
or all of the Other Investors to any such Other Investors or (ii) issue or sell
all or any part of the Participation Securities to any Onex Investor or
Affiliate of an Onex Investor and also issue to any Onex Investor or Affiliate
of an Onex Investor all or any part of the Equityholder Participation Securities
of some or all of the Other Investors.

            If the Participation Securities Offeror elects to issue
Participation Securities to any Onex Investor or Affiliate of an Onex Investor
under this Section 6.4(b) before it delivers a Preemptive Notice, then the
Participation Securities Offeror shall deliver the Preemptive Notice to each
Other Investor no later than ten Business Days after the date on which the
Participation Securities are issued or sold to the Onex Investor or Affiliate of
an Onex Investor. If at the time any Other Investor delivers a timely Exercise
Notice in accordance with Section 6.3, the Participation Securities Offeror has
not yet issued or sold the Equityholder Participation Securities that such Other
Investor is entitled to purchase hereunder to an Onex Investor or Affiliate of
an Onex Investor, then such unissued Equityholder Participation Securities shall
be issued or sold by the Participation Securities Offeror to such Other Investor
as promptly as practicable, but in no event later than five Business Days
following the date of delivery of the Exercise Notice, at the same price, and on
the same terms and conditions, as were applicable to the issuance or sale of
Participation Securities to any Onex Investor or Affiliate of an Onex Investor.

            (c) If at the time an Other Investor delivers a timely Exercise
Notice in accordance with Section 6.3, the Participation Securities Offeror has
issued or sold some or all of the Equityholder Participation Securities that
such Other Investor is entitled to purchase hereunder to any Onex Investor or
Affiliate of an Onex Investor, then any such Equityholder Participation
Securities shall be sold by an Onex Investor or Affiliate of an Onex Investor to
such Other Investor as promptly as is practicable, but in no event later than
five Business Days following the date of delivery of the Exercise Notice, at a
price per Participation Security equal to the price paid by an Onex Investor or
Affiliate of an Onex Investor therefor, plus interest on such amount from the
date of purchase by an Onex Investor or Affiliate of an Onex Investor through
the date of sale to the Other Investor, at a rate per annum equal to the
then-effective prime rate, as announced by Citibank N.A. At the closing of any
such sale by an Onex Investor or Affiliate of an Onex Investor, such Persons
shall deliver to the Other Investor certificates representing the Equityholder
Participation Securities to be conveyed, duly endorsed or accompanied by stock
powers executed in blank, against payment of the purchase price therefor
calculated hereunder.

            (d) If Participation Securities issued or sold by the Participation
Securities Offeror consist of multiple types or classes of securities, then the
Other Investors who elect to exercise their preemptive right shall purchase such
types or classes of securities in the same relative proportions as do Onex
Investors or Affiliates of Onex Investors. Further, if any Participation
Securities to be issued or sold by the Participation Securities Offeror are to
be issued or sold by the Participation Securities Offeror as part of a Units
that includes, or otherwise together with other securities (including debt
securities) of the Participation Securities Offeror

                                       16
<PAGE>

that are not Participation Securities ("OTHER SECURITIES"), then any Other
Investor exercising preemptive rights provided under this Article 6 must in
connection therewith also purchase such Other Securities of the Participation
Securities Offeror that are part of such Units or otherwise being issued or sold
by the Participation Securities Offeror together with the Participation
Securities, and the definitions of "Participation Securities" and "Equityholder
Participation Securities" shall for all purposes of this Article 6 be deemed to
include any such Other Securities of the Participation Securities Offeror.

            6.5 Sale by Participation Securities Offeror Absent Exercise of
Preemptive Right. If, with respect to any issuance or sale of Participation
Securities in connection with which the Participation Securities Offeror has
delivered Preemptive Notices, no Other Investor has delivered a timely Exercise
Notice covering some or all Equityholder Participation Securities that are the
subject of such Preemptive Notices, the Participation Securities Offeror shall,
unless the Participation Securities Offeror has already done so in reliance on
Section 6.4(b), have 120 days following the expiration of the ten Business Day
period following the date of delivery of the Preemptive Notice in which to sell
all or any part of those Equityholder Participation Securities which
Equityholders have not so elected to purchase to any Person or entity, including
but not limited to any Onex Investor or Affiliate of an Onex Investor.

            6.6 Termination; Securities Excluded from Preemptive Right. The
provisions of this Article 6 will terminate automatically upon the earlier to
occur of (a) an Approved Sale or (b) a Qualified Public Offering and shall not
apply to such Approved Sale or Qualified Public Offering. The provisions of this
Article 6 shall not apply to (ii) Participation Securities issued in connection
with a pro rata stock or Unit dividend, stock or Unit split or recapitalization
or the like, (ii) Participation Securities issued upon exercise or conversion of
any Units Equivalent, (iii) Participation Securities issued in a Public Sale or
Public Offering, whether or not any Onex Investor or Affiliate of an Onex
Investor participates in such Public Sale or Public Offering, or (iv)
Participation Securities issued in any transaction or series of related
transactions in which less than 20% of the Participation Securities to be issued
are purchased by Onex Investors or Affiliates of Onex Investors.

                                    ARTICLE 7

                               Transfers of Units

            7.1 Transfers in Accordance with this Agreement. The Company may
refuse to register any transfer of Units on its transfer books if such transfer
is not in accordance with this Agreement and state and federal securities laws.

            7.2 Legending of Units Certificates. The Units may be
uncertificated. All certificates representing Units held by any Person subject
to this Agreement (and by any permitted or required transferees who are bound by
or subject to this Agreement) shall bear the following legend:

                                       17
<PAGE>

            THE SECURITIES REPRESENTED BY THIS CERTIFICATE HAVE NOT BEEN
            REGISTERED UNDER THE SECURITIES ACT OF 1933 AND MAY NOT BE SOLD
            (WITHIN THE MEANING OF SUCH ACT) IN THE ABSENCE OF REGISTRATION
            UNDER SUCH ACT OR AN EXEMPTION THEREFROM. THE SECURITIES REPRESENTED
            BY THIS CERTIFICATE ARE ALSO SUBJECT TO CERTAIN RESTRICTIONS ON
            TRANSFER AND CERTAIN RESTRICTIONS ON THE VOTING OF SUCH SECURITIES
            CONTAINED IN THE INVESTOR EQUITYHOLDERS AGREEMENT, DATED AS OF
            FEBRUARY 10, 2005, AMONG THE ISSUER OF SUCH SECURITIES (THE
            "COMPANY") AND CERTAIN OF THE COMPANY'S EQUITYHOLDERS. A COPY OF
            SUCH INVESTOR EQUITYHOLDERS AGREEMENT WILL BE FURNISHED WITHOUT
            CHARGE BY THE COMPANY TO THE HOLDER HEREOF UPON WRITTEN REQUEST.

            7.3 Default of Delivery.

            (a) In the event that any Equityholder, the Company, or any
Equityholder's transferees or assignees (each, a "REQUIRING PARTY") have the
right to acquire Units from any other Equityholder or the right to require any
such other Equityholder to sell its Units to any other Person, pursuant to the
terms of this Agreement (such selling Equityholder hereinafter referred to as
the "TRANSFEROR" and such Requiring Party or any other Person to whom the
Transferor is required to transfer Units, as applicable, hereinafter referred to
as the "TRANSFEREE") and the Transferor is not present at the closing, or is
present but for any reason fails to produce and deliver to the Transferee the
certificates or other instruments representing any of the Units being
transferred, then the cash purchase price, as and when payable, may be deposited
into a bank account in the name of the Company and any other consideration
permitted or required to be delivered in satisfaction of the purchase price
shall be deposited with the Company. Such deposits shall constitute valid and
effective payment to the Transferor of the purchase price for the Units being
transferred notwithstanding the fact that the Transferor may have voluntarily
attempted to encumber or dispose of any of the Units contrary to the terms
hereof, or that one or more certificates or other evidences of ownership of such
Units may have been delivered to any other Person. From and after the date of
such deposits (even though the Unit certificates in the name of the Transferor
have not been delivered to the Transferee), the purchase by and transfer of the
Units to the Transferee shall be deemed to have been fully completed and all
right, title, benefit and interest of the Transferor in and to all such Units,
both at law and in equity, shall be conclusively deemed to have been transferred
and assigned to and become vested in the Transferee and the Transferee will have
the right to request that the Company enter the transfer into the Unit register
and the Company shall be entitled to so enter the transfer.

                                       18
<PAGE>

            (b) Where the Transferee has made a deposit in accordance with
subsection (a), the Transferor shall be entitled to receive the cash purchase
price of the Units so deposited with the Company's bankers, and to receive any
other consideration deposited with the Company. Upon delivery to the Company of
(i) the certificates or other instruments representing the Units duly endorsed
for transfer and (ii) any other document required to be delivered by the
Transferor at closing, including, without limitation, the release or discharge
of any encumbrance relating to the Units and stock transfer stamps, if
necessary.

                                    ARTICLE 8

                                  Miscellaneous

            8.1 Voting Agreement and Appointment of Proxy.

            (a) The Other Investors shall at all times vote their Units (to the
extent they are entitled to vote the same) as specifically provided herein or,
if not so provided, in the same manner as the Units held by the Majority Onex
Investors are voted, on the election of directors and on all other matters which
are submitted to a vote (or consent in lieu of voting) of the Company's
equityholders and on which such Units are entitled to vote. To the extent
permitted by law and for all purposes of this Agreement, each Other Investor, by
its execution of this Agreement, hereby irrevocably constitutes and appoints
Onex Partners and such other Persons as may from time to time be designated by
the Majority Onex Investors, its proxy with full power of substitution to vote
all of its Units at any meeting of equityholders of the Company, or to give
consent in lieu of voting on the election of directors and on any matter which
is submitted for a vote or consent to the equityholders and on which such Units
are entitled to vote, provided, that such Units are voted or consent is given
with respect to it as specifically provided herein, or if not so provided, in
the same manner as the Units held by the Majority Onex Investors. The proxies
and powers granted by the Other Investors pursuant to this Section 8.1 are
coupled with an interest.

            (b) Each Equityholder represents that it has not granted and is not
a party to any proxy, voting trust or other agreement which is inconsistent with
or conflicts with the provisions of this Agreement, and no such holder of Units
shall grant any proxy or become party to any voting trust or other agreement
which is inconsistent with or conflicts with the provisions of this Agreement.

            (c) The voting agreement set forth in this Section 8.1 shall
terminate automatically upon an Approved Sale.

            8.2 Notices. All notices, consents and other communications required
or permitted to be given under or by reason of this Agreement shall be in
writing, shall be delivered personally or by e- mail or telecopy as described
below or by reputable overnight courier, and shall be deemed given on the date
on which such delivery is made, provided, that any such delivery made on a day
that is not a Business Day, or that is made after 5:00 p.m. on a Business

                                       19
<PAGE>

Day, shall be deemed to be given on the following Business Day. If delivered by
e-mail or telecopy, such notices or communications shall be confirmed by a
registered or certified letter (return receipt requested), postage prepaid. Any
such delivery shall be addressed to the intended recipient at the following
addresses (or at such other address for a party as shall be specified by such
party by like notice to the other parties):

            If to the Company:                Emergency Medical Services L.P.
                                              1717 Main Street, Suite 5200
                                              Dallas, TX 75201
                                              Attention: Chief Executive Officer
                                              Fax: (214) 712-2005

                  with a copy to:             Onex Investment Corp.
                                              712 Fifth Avenue
                                              New York, New York  10019
                                              Attention:  Robert M. Le Blanc
                                              Fax:  (212) 582-0909

            If to an Onex Investor:           c/o Onex Investment Corp.
                                              712 Fifth Avenue
                                              New York, New York  10019
                                              Attention:  Robert M. Le Blanc
                                              Fax:  (212) 582-0909

                  with copies to:             Onex American Holdings II LLC
                                              21 Leader Street
                                              Marion, Ohio  43302
                                              Attention:  Donald F. West
                                              Fax:  (740) 223-7762

                  and                         Kaye Scholer LLP
                                              425 Park Avenue
                                              New York, New York  10022
                                              Attention:  Joel I. Greenberg
                                              and Lynn Toby Fisher
                                              Fax:  (212) 836-8689

            If to any Other Investor at such Other Investor's address as set
forth on such Other Investor's signature page hereto.

            If to any other Person which becomes a party to this Agreement in
accordance with the terms hereof, at the address for delivery of notices or
communications given to all other parties by such party at such time.

            8.3 Interpretation. In this Agreement, unless a contrary intention
appears, (a) the words "herein," "hereof" and "hereunder" and other words of
similar import refer to this Agreement as a whole and not to any particular
Article, Section or other subdivision, (b) the words "include," "includes" or
"including" shall be deemed to be followed by the words "without limitation,"
(c) reference to any Article or Section means such Article or Section hereof,

                                       20
<PAGE>

(d) words of any gender shall be deemed to include each other gender, and (e)
words using the singular or plural number shall also include the plural or
singular number, respectively. No provision of this Agreement shall be
interpreted or construed against any party hereto solely because such party or
its legal representative drafted such provision.

            8.4 Captions. The captions in this Agreement are for convenience of
reference only and shall not be given any effect in the interpretation of this
Agreement.

            8.5 Governing Law. This Agreement shall be construed in accordance
with, and governed by, the laws of the State of Delaware without regard to
conflicts of laws principles which would result in the application of the laws
of another jurisdiction.

            8.6 Time. Time shall be of the essence of this Agreement.

            8.7 Severability. If any provision of this Agreement is held invalid
or unenforceable by any court of competent jurisdiction, the other provisions of
this Agreement will remain in full force and effect. Any provision of this
Agreement held invalid or unenforceable only in part or degree will remain in
full force and effect to the extent not held invalid or unenforceable.

            8.8 Jurisdiction. The parties hereby irrevocably and unconditionally
consent to submit to the exclusive jurisdiction of the courts of the State of
Delaware and the United States District Court for the District of Delaware for
any actions, suits or proceedings arising out of or relating to this agreement
and the transactions contemplated hereby (and agree not to commence any action,
suit or proceeding relating thereto except in such courts). The parties hereby
irrevocably and unconditionally waive any objection to the laying of venue of
any action, suit or proceeding arising out of this Agreement or the transactions
contemplated hereby in the courts of the State of Delaware and the United States
District Court from the District of Delaware, and hereby further irrevocably and
unconditionally waive and agree not to plead or claim in any such court that any
such action, suit or proceeding brought in any such court has been brought in an
inconvenient forum.

            8.9 Waiver of Jury Trial. EACH OF THE PARTIES HERETO IRREVOCABLY
WAIVES ANY AND ALL RIGHT TO TRIAL BY JURY IN ANY LEGAL PROCEEDING ARISING OUT OF
OR RELATED TO THIS AGREEMENT OR THE TRANSACTIONS CONTEMPLATED HEREBY.

            8.10 Assignment. This Agreement shall be binding upon the parties
hereto, all Equityholders and, to the extent expressly provided elsewhere in
this Agreement, their respective permitted transferees and assigns (other than
purchasers of equity securities pursuant to a Public Sale), together with in
each case all successors, heirs, executors and administrators thereof, and shall
inure to the benefit of the parties hereto, all Equityholders and, to the extent
expressly provided elsewhere in this Agreement, assigns of the Equityholders,
together, in each case, with

                                       21
<PAGE>

all successors, heirs, executors and administrators thereof. Except as otherwise
provided herein, no party may assign any of its rights or delegate any of its
duties under this Agreement.

            8.11 Amendment and Waiver. Except as otherwise provided herein, no
modification, amendment or waiver of any provision of this Agreement will be
effective unless such modification, amendment or waiver is approved in writing
by the Company, the Majority Onex Investors and Other Investors holding a
majority of the Units held by all Other Investors, provided, that a
modification, amendment or waiver of Section 4.3(b) as to any Other Investor may
be authorized by such Other Investor and the Board. The failure of a party to
insist upon strict adherence to any term of this Agreement on any occasion shall
not be considered a waiver or deprive that party of the right thereafter to
insist upon strict adherence to that term or any other term of this Agreement.
No purported waiver shall be effective unless in writing. The waiver by any
party of a breach of any provision of this Agreement shall not operate or be
construed as a waiver of any subsequent or other breach.

            8.12 Remedies. The parties shall be entitled to enforce their rights
under this Agreement specifically to recover damages by reason of any breach of
any provision of this Agreement and to exercise all other rights existing in
their favor. The parties hereto agree and acknowledge that money damages may not
be an adequate remedy for any breach of the provisions of this Agreement and
that any party may in its sole discretion apply to any court of law or equity of
competent jurisdiction for specific performance and/or temporary, preliminary or
permanent injunctive relief (without posting a bond or other security) in order
to enforce or prevent any violation of the provisions of this Agreement.

            8.13 Counterparts; Joinder. This Agreement may be executed in
counterparts, each of which shall be considered an original, but all of which
together shall constitute one and the same instrument. Additional Persons may
become parties to this Agreement in accordance with the provisions of this
Agreement or with the consent of the Company and the Majority Onex Investors, in
either case by executing and delivering to the Company a joinder agreement.

            8.14 Complete Agreement. This Agreement, the documents expressly
referred to herein (including the Registration Agreement) and other documents of
even date herewith embody the complete agreement and understanding among the
parties and supersede and preempt any prior understanding, agreements or
representations by or among the parties, written or oral, that may be related to
the subject matter hereof in any way.

                            [Signature Pages Follows]

                                       22
<PAGE>

            IN WITNESS WHEREOF, this Agreement has been duly executed by the
parties hereto, all as of the date first above written.

                 EMERGENCY MEDICAL SERVICES L.P.

                 By: Emergency Medical Services Corporation, its general partner

                 By: /s/ Robert M. Le Blanc
                     -----------------------------------------------------------
                     Name:  Robert M. Le Blanc
                     Title: President

                 ONEX AMERICAN HOLDINGS II LLC

                 By: /s/ Donald F. West
                     -----------------------------------------------------------
                     Name:  Donald F. West
                     Title: Director

                 By: /s/ Eric J. Rosen
                     -----------------------------------------------------------
                     Name:  Eric J. Rosen
                     Title: Director

                 ONEX US PRINCIPALS LP

                 By:   Onex American Holdings GP LLC, its General Partner

                 By: /s/ Donald F. West
                     -----------------------------------------------------------
                     Name:  Donald F. West
                     Title: Representative

                 EMS EXECUTIVE INVESTCO LLC

                 By: /s/ Donald F. West
                     -----------------------------------------------------------
                     Name:  Donald F. West
                     Title: Director

              [Signature Page to Investor Equityholders Agreement]

<PAGE>



                 ONEX EMSC CO-INVEST LP

                 By: Onex Partners GP LP, its General Partner
                 By: Onex Partners Manager LP, its Agent
                 By: Onex Partners Manager GP Inc., its General Partner

                 By: /s/ Robert M. Le Blanc
                     -----------------------------------------------------------
                     Name:  Robert M. Le Blanc
                     Title: Managing Director

                 By: /s/ Eric J. Rosen
                     -----------------------------------------------------------
                     Name:  Eric J. Rosen
                     Title: Managing Director

                 ONEX PARTNERS LP

                 By:   Onex Partners GP LP, its General Partner
                 By:   Onex Partners Manager LP, its Agent
                 By:  Onex Partners Manager GP Inc., its General Partner

                 By: /s/ Robert M. Le Blanc
                     -----------------------------------------------------------
                     Name:  Robert M. Le Blanc
                     Title: Managing Director

                 By: /s/ Eric J. Rosen
                     -----------------------------------------------------------
                     Name:  Eric J. Rosen
                     Title: Managing Director

              [Signature Page to Investor Equityholders Agreement]
<PAGE>

           IN WITNESS WHEREOF, this Agreement has been duly executed by the
undersigned.

Dated: April 22, 2005

                 OTHER INVESTOR

                 /s/ Steven B. Epstein
                 ---------------------------------------------------------------

                 Name: Steven B. Epstein

                 Address: 10105 Iron Gate Rd.

                          Potomac, MD 20854

                 _______________________________________________________________

    [Signature page (joinder agreement) to Investor Equityholders Agreement]

<PAGE>

            IN WITNESS WHEREOF, this Agreement has been duly executed by the
undersigned.

Dated: As of February 10, 2005

                 OTHER INVESTOR

                 /s/ Steve Shulman
                 ---------------------------------------------------------------

                 Name: Steve Shulman

                 Address: 39 Hazen Dr.

                          Avon, CT 06001

                 _______________________________________________________________

    [Signature page (joinder agreement) to Investor Equityholders Agreement]

<PAGE>

            IN WITNESS WHEREOF, this Agreement has been duly executed by the
parties hereto, all as of the date first above written.

                 OTHER INVESTOR

                 /s/ Angel L. Iscovich
                 ---------------------------------------------------------------

                 Name: Angel L. Iscovich

                 Address: 4025 Lago Drive

                          Santa Barbara, CA  93110

                 _______________________________________________________________

    [Signature page (joinder agreement) to Investor Equityholders Agreement]

<PAGE>

            IN WITNESS WHEREOF, this Agreement has been duly executed by the
parties hereto, all as of the date first above written.

                 OTHER INVESTOR

                 /s/ Joseph Taylor
                 ---------------------------------------------------------------

                 Name: Joseph Taylor

                 Address: ______________________________________________________

                 _______________________________________________________________

                 _______________________________________________________________

    [Signature page (joinder agreement) to Investor Equityholders Agreement]

<PAGE>

            IN WITNESS WHEREOF, this Agreement has been duly executed by the
parties hereto, all as of the date first above written.

                 OTHER INVESTOR

                 /s/ Terry R. Meadows
                 ---------------------------------------------------------------

                 Name: Terry R. Meadows

                 Address: 2856 Kensington Trace

                          Tarpon Springs, FL  34688-8419

                 _______________________________________________________________

    [Signature page (joinder agreement) to Investor Equityholders Agreement]

<PAGE>

            IN WITNESS WHEREOF, this Agreement has been duly executed by the
parties hereto, all as of the date first above written.

                 OTHER INVESTOR

                 /s/ Douglas P. Webster
                 ---------------------------------------------------------------

                 Name: Douglas P. Webster

                 Address: 2020 N. Lincoln Park West #38 DEF

                          Chicago, IL  60614

                 _______________________________________________________________

    [Signature page (joinder agreement) to Investor Equityholders Agreement]

<PAGE>

            IN WITNESS WHEREOF, this Agreement has been duly executed by the
parties hereto, all as of the date first above written.

                 OTHER INVESTOR

                 /s/ Louis K. Meyer
                 ---------------------------------------------------------------

                 Name: Louis K. Meyer

                 Address: 10644 N. Oakwilde Ave.

                          Stockton, CA  95212

                 _______________________________________________________________

    [Signature page (joinder agreement) to Investor Equityholders Agreement]

<PAGE>

            IN WITNESS WHEREOF, this Agreement has been duly executed by the
parties hereto, all as of the date first above written.

                 OTHER INVESTOR

                 /s/ James L. Murphy
                 ---------------------------------------------------------------

                 Name: James L. Murphy

                 Address: 1200 Whispering Lane

                          Southlake, TX  76092

                 _______________________________________________________________

    [Signature page (joinder agreement) to Investor Equityholders Agreement]

<PAGE>

            IN WITNESS WHEREOF, this Agreement has been duly executed by the
parties hereto, all as of the date first above written.

                 OTHER INVESTOR

                 /s/ Don S. Harvey
                 ---------------------------------------------------------------

                 Name: Don S. Harvey

                 Address: 7762 Sandhill Ct.

                          West Palm Beach, FL  33412

                 _______________________________________________________________

    [Signature page (joinder agreement) to Investor Equityholders Agreement]

<PAGE>

            IN WITNESS WHEREOF, this Agreement has been duly executed by the
parties hereto, all as of the date first above written.

                 OTHER INVESTOR

                 /s/ William A. Sanger
                 ---------------------------------------------------------------
                 Name: William A. Sanger

                 Address: 430 Steele St.

                          Denver, CO  80206

                 _______________________________________________________________

    [Signature page (joinder agreement) to Investor Equityholders Agreement]

<PAGE>

            IN WITNESS WHEREOF, this Agreement has been duly executed by the
parties hereto, all as of the date first above written.

                 OTHER INVESTOR

                 /s/ Dighton Packard
                 ---------------------------------------------------------------

                 Name: Dighton Packard

                 Address: 6903 Lyre Lane

                          Dallas, TX  75214

                 _______________________________________________________________

    [Signature page (joinder agreement) to Investor Equityholders Agreement]

<PAGE>

            IN WITNESS WHEREOF, this Agreement has been duly executed by the
parties hereto, all as of the date first above written.

                 OTHER INVESTOR

                 /s/ Todd Zimmerman
                 ---------------------------------------------------------------
                 Name: Todd Zimmerman

                 Address: 1420 Sandstone Ct.

                          Southlake, TX  76092

                 _______________________________________________________________

    [Signature page (joinder agreement) to Investor Equityholders Agreement]

<PAGE>

            IN WITNESS WHEREOF, this Agreement has been duly executed by the
parties hereto, all as of the date first above written.

                 OTHER INVESTOR

                 /s/ David Mintz
                 ---------------------------------------------------------------

                 Name: David Mintz

                 Address: 2006 Havemeyer Lane

                          Redondo Beach, CA  90278

                 _______________________________________________________________

    [Signature page (joinder agreement) to Investor Equityholders Agreement]

<PAGE>

            IN WITNESS WHEREOF, this Agreement has been duly executed by the
parties hereto, all as of the date first above written.

                 OTHER INVESTOR

                 /s/ Steve W. Ratton, Jr.
                 ---------------------------------------------------------------

                 Name: Steve W. Ratton, Jr.

                 Address: 692 Allen Rd.

                          Coppell, Tx  75019

                 _______________________________________________________________

    [Signature page (joinder agreement) to Investor Equityholders Agreement]

<PAGE>

            IN WITNESS WHEREOF, this Agreement has been duly executed by the
parties hereto, all as of the date first above written.

                 OTHER INVESTOR

                 /s/ Randel G. Owen
                 ---------------------------------------------------------------

                 Name: Randel G. Owen

                 Address: 944 Aztec Dr.

                          Castle Rock, CO  80108

                 _______________________________________________________________

    [Signature page (joinder agreement) to Investor Equityholders Agreement]

<PAGE>

            IN WITNESS WHEREOF, this Agreement has been duly executed by the
parties hereto, all as of the date first above written.

                 OTHER INVESTOR

                 /s/ Russell H. Harris MD
                 ---------------------------------------------------------------

                 Name: Russell H. Harris MD

                 Address: 5829 Wissahiclem Ave.

                          Philadelphia, PA  19144

                 _______________________________________________________________

    [Signature page (joinder agreement) to Investor Equityholders Agreement]

<PAGE>

            IN WITNESS WHEREOF, this Agreement has been duly executed by the
undersigned.

Dated: March 10, 2005

                 OTHER INVESTOR

                 /s/ James T. Kelly
                 ---------------------------------------------------------------

                 Name: James T. Kelly

                 Address: 64 Boggs Hill Rd

                          Newtown, CT  06470

                 _______________________________________________________________

    [Signature page (joinder agreement) to Investor Equityholders Agreement]

<PAGE>

  IN WITNESS WHEREOF, this Agreement has been duly executed by the undersigned.

Dated: June 30, 2005

                 OTHER INVESTOR

                 /s/ Michael L. Smith
                 ---------------------------------------------------------------

                 Name: Michael L. Smith

                 Address:  4975 Deer Ridge Dr. So.

                           Carmel, Indiana 46033

                 _______________________________________________________________