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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

                 _______________________________________________________________<PAGE>

                                                                     Exhibit 4.5

                             REGISTRATION AGREEMENT

      THIS AGREEMENT is made as of February 10, 2005, among Emergency Medical
Services L.P., a Delaware limited partnership (the "COMPANY"), and the Persons
listed on Schedule A attached hereto and such other equityholders of the Company
as may, from time to time, become parties to this Agreement in accordance with
the provisions hereof (the "INVESTORS").

      Upon consummation of (i) 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., (ii) 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., and of certain related transactions to
be consummated concurrently therewith, Onex Partners and certain other
equityholders will own or may hereafter acquire units representing limited
partnership interests in the Company (the "UNITS"). In order to induce Investors
to purchase Units by subscription, through the exercise of options or otherwise
the Company has agreed to provide the registration rights set forth in this
Agreement.

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

      1.    Demand Registrations.

            (a)   Requests for Registration. Subject to Sections 1(b) and 1(c),
at any time after the Reorganization Date, the Majority Onex Investors may
request registration under the Securities Act of all or part of their
Registrable Securities on Form S-1 or any similar long-form registration
("LONG-FORM REGISTRATIONS") or, if available, on Form S-2 or S-3 or any similar
short-form registration ("SHORT-FORM REGISTRATIONS"). In addition, at any time
after the consummation of a Public Offering, the holders of a majority of the
Registrable Securities may request Long-Form Registrations or, if available,
Short-Form Registrations of all or part of their Registrable Securities until
such holders cease to hold at least 10% of the number of Registrable Securities
held by such holders as of the date hereof. Each request for a registration
under this Section 1(a) shall specify the approximate number of Registrable
Securities requested to be registered and the proposed method of distribution.
Within ten days after receipt of any such request, the Company will give written
notice of such requested registration to all other holders of Registrable
Securities and, subject to Section 1(d), will include in such registration all
Registrable Securities with respect to which the Company has received written
requests for inclusion therein within 15 days after the receipt of the Company's
notice. All registrations requested pursuant to this Section 1(a) are referred
to herein as "DEMAND REGISTRATIONS."

            (b)   Long-Form Registrations. The holders of a majority of the
Registrable Securities will be entitled to request three Long-Form Registrations
in which the Company will pay all Registration Expenses and the Majority Onex
Investors will be entitled to request an unlimited number of Long-Form
Registrations in which the Company will pay all Registration Expenses
("COMPANY-PAID LONG-FORM REGISTRATIONS"). A registration will not count as one
of the permitted Long-Form Registrations until it has become effective (unless
such Long-Form Registration has not become effective due solely to the fault of
the holders requesting such registration and such holders

<PAGE>

do not agree to bear all Registration Expenses in connection therewith);
provided, that in any event (absent such an agreement by the holders requesting
such registration) the Company will pay all Registration Expenses in connection
with any registration initiated as a Company-Paid Long-Form Registration whether
or not it has become effective. All Long-Form Registrations shall be
underwritten registrations.

            (c)   Short-Form Registrations. In addition to the Company-Paid
Long-Form Registrations provided pursuant to Section 1(b), the Majority Onex
Investors and the holders a majority of the Registrable Securities will each be
entitled to request an unlimited number of Short-Form Registrations in which the
Company will pay all Registration Expenses. Demand Registrations will be
Short-Form Registrations whenever the Company is permitted to use any applicable
short form. After the Company has become subject to the reporting requirements
of the Securities Exchange Act, the Company will use its commercially reasonable
efforts to be eligible to use Short-Form Registrations for the sale of
Registrable Securities.

            (d)   Priority on Demand Registrations. The Company will not include
in any Demand Registration any securities that are not Registrable Securities
without the prior written consent of the holders of at least a majority of the
Registrable Securities included in such registration. If a Demand Registration
is an underwritten offering and the managing underwriters advise the Company in
writing that in their opinion the number of Registrable Securities and, if
permitted pursuant to the immediately preceding sentence, other securities
requested to be included in such offering exceeds the number of Registrable
Securities and other securities, if any, which can be sold therein without
adversely affecting the marketability of the offering, the Company will include
in such registration prior to the inclusion of any securities which are not
Registrable Securities the number of Registrable Securities requested to be
included (whether upon exercise of a demand registration right or upon exercise
of the right to participate in such a demand registration) that in the opinion
of such underwriters can be sold without adversely affecting the marketability
of the offering, pro rata among the respective holders thereof on the basis of
the number of Registrable Securities requested to be included by each such
holder.

            (e)   Restrictions on Demand Registrations. The Company will not be
obligated to effect any Demand Registration within six months after the
effective date of a Demand Registration or a registration in which the holders
of Registrable Securities were given piggyback rights pursuant to Section 2 and
in which there was no reduction in the number of Registrable Securities
requested to be included. The Company may postpone for up to six months the
filing or the effectiveness of a registration statement for a Demand
Registration if the Board of Directors of the Company determines that such
Demand Registration would reasonably be expected to have an adverse effect on
(i) any proposal or plan by the Company or any of its subsidiaries to engage in
any acquisition of assets (other than in the ordinary course of business) or any
merger, consolidation, tender offer or similar transaction, or (ii) any material
corporate development; provided that in such event, the holders of Registrable
Securities initially requesting such Demand Registration will be entitled to
withdraw such request and, if such request is withdrawn, such Demand
Registration will not count as a requested Demand Registrations hereunder and
the Company will pay all Registration Expenses in connection with such
registration.

<PAGE>

            (f)   Selection of Underwriters. The holders of a majority of the
Registrable Securities included in any Demand Registration will have the right
to select the investment banker(s) and manager(s) to administer the offering,
subject to the Company's approval which will not be unreasonably withheld.

            (g)   Other Registration Rights. The Company will not grant to any
Persons the right to request the Company to register any equity securities of
the Company, or any securities convertible or exchangeable into or exercisable
for such securities, without the prior written consent of the holders of at
least a majority of the Registrable Securities; provided, that the Company may
grant rights to other Persons to participate in Piggyback Registrations or
Demand Registrations so long as such rights are subordinate to the rights of the
holders of Registrable Securities with respect to such Piggyback Registrations
or Demand Registrations.

      2.    Piggyback Registrations.

            (a)   Right to Piggyback. Whenever the Company proposes to register
any of its securities under the Securities Act (including primary registrations
on behalf of the Company and secondary registrations on behalf of the holders of
its securities other than pursuant to a Demand Registration) and the
registration form to be used may be used for the registration of Registrable
Securities (a "PIGGYBACK REGISTRATION"), the Company will give prompt written
notice to all holders of Registrable Securities of its intention to effect such
a registration and will include in such registration all Registrable Securities
with respect to which the Company has received written requests for inclusion
therein within 15 days after the receipt of the Company's notice.

            (b)   Piggyback Expenses. The Registration Expenses of the holders
of Registrable Securities will be paid by the Company in all Piggyback
Registrations.

            (c)   Priority on Primary Registrations. If a Piggyback Registration
is an underwritten primary registration on behalf of the Company, and the
managing underwriters advise the Company in writing that in their opinion the
number of securities requested to be included in such registration exceeds the
number which can be sold in such offering without adversely affecting the
marketability of the offering, the Company will include in such registration (i)
first, the securities the Company proposes to sell, (ii) second, the Registrable
Securities requested to be included in such registration, pro rata among the
holders of such Registrable Securities on the basis of the number of shares
requested to be included by each such holder, and (iii) third, other securities
requested to be included in such registration.

            (d)   Priority on Secondary Registrations. If a Piggyback
Registration is an underwritten secondary registration on behalf of holders of
the Company's securities, and the managing underwriters advise the Company in
writing that in their opinion the number of securities requested to be included
in such registration exceeds the number which can be sold in such offering
without adversely affecting the marketability of the offering, the Company will
include in such registration (i) first, pro rata among the securities requested
to be included therein by the holders requesting such registration and the other
Registrable Securities requested to be included in such registration, on the
basis of the number of shares requested to be included by each such holder, and
(ii) second, other securities requested to be included in such registration.

                                        3

<PAGE>

            (e)   Selection of Underwriters. If any Piggyback Registration is an
underwritten offering, the selection of investment banker(s) and manager(s) for
the offering must be approved by the holders of a majority of the Registrable
Securities included in such Piggyback Registration. Such approval will not be
unreasonably withheld.

            (f)   Other Registrations. If the Company has previously filed a
registration statement with respect to Registrable Securities pursuant to
Section 1 or pursuant to this Section 2, and if such previous registration has
not been withdrawn or abandoned, the Company will not, except as required by
Section 1, file or cause to be effected any other registration of any of its
equity securities or securities convertible or exchangeable into or exercisable
for its equity securities under the Securities Act (except on Form S-8 or Form
S-4 or any successor forms), whether on its own behalf or at the request of any
holder or holders of such securities, until a period of at least six months has
elapsed from the effective date of such previous registration.

      3.    Holdback Agreements.

            (a)   Each holder of Registrable Securities agrees not to effect any
public sale or distribution (including sales pursuant to Rule 144 under the
Securities Act) of Registrable Securities of the Company, or any securities
convertible into or exchangeable or exercisable for such securities, during the
seven days prior to and the 90-day (180-day in the case of the initial Public
Offering) period beginning on the effective date of any underwritten Demand
Registration or any underwritten Piggyback Registration in which Registrable
Securities are included or which is the initial Public Offering (except as part
of such underwritten registration), unless the underwriters managing the
registered public offering otherwise agree.

            (b)   The Company agrees (i) not to effect any public sale or
distribution of its equity securities, or any securities convertible into or
exchangeable or exercisable for such securities, during the seven days prior to
and during the 90-day period beginning on the effective date of any underwritten
Demand Registration or any underwritten Piggyback Registration (except as part
of such underwritten registration or pursuant to registrations on Form S-8 or
S-4 or any successor form), unless the underwriters managing the registered
public offering otherwise agree, and (ii) to cause each holder of its common
stock, or any securities convertible into or exchangeable or exercisable for
common stock, purchased from the Company at any time after the date of this
Agreement (other than in a registered public offering) to agree not to effect
any public sale or distribution (including sales pursuant to Rule 144 under the
Securities Act) of any Registrable Securities during such period (except as part
of such underwritten registration, if otherwise permitted), unless the
underwriters managing the registered public offering otherwise agree.

      4.    Registration Procedures. Whenever the holders of Registrable
Securities have requested that any Registrable Securities be registered pursuant
to this Agreement, the Company will use commercially reasonable efforts to
effect the registration and the sale of such Registrable Securities in
accordance with the intended method of disposition thereof, and pursuant thereto
the Company will as expeditiously as possible:

            (a)   prepare and file with the Securities and Exchange Commission a
registration statement with respect to such Registrable Securities and use its
commercially reasonable efforts to cause such registration statement to become
effective (provided that, before filing a registration

                                        4

<PAGE>

statement or prospectus or any amendments or supplements thereto, the Company
will furnish to the counsel selected by the holders of a majority of the
Registrable Securities covered by such registration statement copies of all such
documents proposed to be filed, which documents will be subject to the review of
such counsel);

            (b)   prepare and file with the Securities and Exchange Commission
such amendments and supplements to such registration statement and the
prospectus used in connection therewith as may be necessary to keep such
registration statement effective for the period required to accomplish the plan
of distribution set forth therein (but not more than six months) and comply with
the provisions of the Securities Act with respect to the disposition of all
securities covered by such registration statement during such period in
accordance with the intended methods of disposition by the sellers thereof set
forth in such registration statement;

            (c)   furnish to each seller of Registrable Securities such number
of copies of such registration statement, each amendment and supplement thereto,
the prospectus included in such registration statement (including each
preliminary prospectus) and such other documents as such seller may reasonably
request in order to facilitate the disposition of the Registrable Securities
owned by such seller;

            (d)   use its commercially reasonable efforts to register or qualify
such Registrable Securities under such other securities or blue sky laws of such
jurisdictions as any seller reasonably requests and do any and all other acts
and things which may be reasonably necessary or advisable to enable such seller
to consummate the disposition in such jurisdictions of the Registrable
Securities owned by such seller (provided, that the Company will not be required
to (i) qualify generally to do business in any jurisdiction, (ii) subject itself
to taxation in any such jurisdiction or (iii) consent to general service of
process in any such jurisdiction, in each case where it would not otherwise be
required to qualify, subject itself to taxation or consent to general service of
process but for this subparagraph);

            (e)   notify each seller of such Registrable Securities, at any time
when a prospectus relating thereto is required to be delivered under the
Securities Act, of the happening of any event as a result of which the
prospectus included in such registration statement contains an untrue statement
of a material fact or omits any fact necessary to make the statements therein
not misleading, and, at the request of any such seller, the Company will
promptly prepare a supplement or amendment to such prospectus so that, as
thereafter delivered to the purchasers of such Registrable Securities, such
prospectus will not contain an untrue statement of a material fact or omit to
state any fact necessary to make the statements therein not misleading;

            (f)   cause all such Registrable Securities to be listed on each
securities exchange on which similar securities issued by the Company are then
listed and, if not so listed, to be listed, if eligible for such listing, on one
or more securities exchanges or the NASD automated quotation system (on the
National Market System if the Company so qualifies);

            (g)   provide a transfer agent and registrar for all such
Registrable Securities not later than the effective date of such registration
statement;

                                        5

<PAGE>

            (h)   enter into such customary agreements (including underwriting
agreements in customary form) and take all such other actions as the
underwriters reasonably request in order to expedite or facilitate the
disposition of such Registrable Securities (including, without limitation,
effecting a stock split or a combination of shares);

            (i)   make available for inspection by any seller of Registrable
Securities, any underwriter participating in any disposition pursuant to such
registration statement and any attorney, accountant or other agent retained by
any such seller or underwriter, all financial and other records, pertinent
corporate documents and properties of the Company, and cause the Company's
officers, directors, employees and independent accountants to supply all
information reasonably requested by any such seller, underwriter, attorney,
accountant or agent in connection with such registration statement;

            (j)   otherwise use its commercially reasonable efforts to comply
with all applicable rules and regulations of the Securities and Exchange
Commission, and make available to its security holders, as soon as reasonably
practicable, an earnings statement covering the period of at least twelve months
beginning with the first day of the Company's first full calendar quarter after
the effective date of the registration statement, which earnings statement shall
satisfy the provisions of Section 11(a) of the Securities Act and Rule 158
thereunder;

            (k)   in the event of the issuance of any stop order suspending the
effectiveness of a registration statement, or of any order suspending or
preventing the use of any related prospectus or suspending the qualification of
any common stock included in such registration statement for sale in any
jurisdiction, the Company will use its reasonable best efforts promptly to
obtain the withdrawal of such order;

            (l)   obtain comfort letters, dated (i) the effective date of such
registration statement, (ii) the date the Registrable Securities being sold are
delivered to the underwriters, if any, for sale pursuant thereto and (iii) if
required by the underwriters, if any, on or prior to the date of any preliminary
prospectuses, from the Company's independent public accountants in customary
form and covering such matters of the type customarily covered by comfort
letters and if the Registrable Securities included in such registration
statement constitute at least 10% of the securities covered by such registration
statement, also covering such matters as the holders of a majority of the
Registrable Securities being sold reasonably request;

            (m)   provide a legal opinion of the Company's outside counsel with
respect to the registration statement, each amendment and supplement thereto,
the prospectus included therein (including the preliminary prospectus) and such
other documents relating thereto in customary form and covering such matters of
the type customarily covered by legal opinions of such nature;

            (n)   if requested by the managing underwriter or underwriters or a
holder of Registrable Securities being sold in connection with an underwritten
offering, promptly incorporate in a prospectus supplement or post-effective
amendment such information as the managing underwriters and the holders of a
majority of the Registrable Securities being sold agree should be included
therein relating to the plan of distribution with respect to such Registrable
Securities, including, without limitation, information with respect to the
number of Registrable Securities being sold to such underwriters, the purchase
price being paid therefor by such underwriters and with

                                        6

<PAGE>

respect to any other terms of the underwritten (or best efforts underwritten)
offering of the Registrable Securities to be sold in such offering; and make all
required filings of such prospectus supplement or post-effective amendment as
soon as notified of the matters to be incorporated in such prospectus supplement
or post-effective amendment;

            (o)   cooperate with the selling holders of Registrable Securities
and the managing underwriters, if any, to facilitate the timely preparation and
delivery of certificates representing Registrable Securities to be sold and not
bearing any restrictive legends; and enable such Registrable Securities to be in
such denominations and registered in such names as the managing underwriters may
request at least two business days prior to any sale of Registrable Securities
to the underwriters;

            (p)   cooperate with, and make members of management available to
participate in, road shows and other marketing activities as reasonably
requested by the managing underwriter or underwriters; and

            (q)   use its commercially reasonable efforts to cause the
Registrable Securities covered by the applicable registration statement to be
registered with or approved by such other governmental agencies or authorities
as may be necessary to enable the seller or sellers thereof or the underwriters,
if any, to consummate the disposition of such Registrable Securities.

      5.    Registration Expenses.

            (a)   All expenses incident to the Company's performance of or
compliance with this Agreement, including, without limitation, all registration
and filing fees, fees and expenses associated with filings required to be made
with the NASD (including, if applicable, the fees and expenses of any "qualified
independent underwriter"and its counsel as may be required by the rules and
regulations of the NASD), fees and expenses of compliance with securities or
blue sky laws, printing expenses, messenger and delivery expenses and fees and
disbursements of counsel for the Company and all independent certified public
accountants, underwriters (excluding discounts and commissions) and other
Persons retained by the Company (all such expenses being herein called
"REGISTRATION EXPENSES"), will be borne as provided in this Agreement, except
that the Company will, in any event, pay its internal expenses (including,
without limitation, all salaries and expenses of its officers and employees
performing legal or accounting duties), the expense of any annual audit or
quarterly review, the expense of any liability insurance and the expenses and
fees for listing the securities to be registered on each securities exchange on
which similar securities issued by the Company are then listed or on the NASD
automated quotation system (on the National Market System if the Company so
qualifies).

            (b)   In connection with each Demand Registration and each Piggyback
Registration, the Company will reimburse the holders of Registrable Securities
covered by such registration for the reasonable fees and disbursements of one
counsel chosen by the holders of a majority of the Registrable Securities
initially requesting such registration (in the case of a Demand Registration) or
the holders of a majority of the Registrable Securities included in such
registration (in the case of a Piggyback Registration).

            (c)   To the extent Registration Expenses are not required to be
paid by the Company, each holder of securities included in any registration
hereunder will pay those Registration

                                        7

<PAGE>

Expenses allocable to the registration of such holder's securities so included,
and any Registration Expenses not so allocable will be borne by all sellers of
securities included in such registration in proportion to the aggregate selling
price of the securities to be so registered.

      6.    Indemnification.

            (a)   The Company agrees to indemnify, to the extent permitted by
law, each holder of Registrable Securities, its officers and directors and each
Person who controls such holder (within the meaning of the Securities Act or the
Securities Exchange Act) against all losses, claims, damages, liabilities and
expenses (including any amounts paid in any settlement effected with the
Company's consent, which consent shall not be unreasonably withheld) caused by
any untrue or alleged untrue statement of material fact contained in any
registration statement, prospectus or preliminary prospectus or any amendment
thereof or supplement thereto or any omission or alleged omission of a material
fact required to be stated therein or necessary to make the statements therein
not misleading or any violation by the Company of any federal, state or common
law risk applicable to the Company and relating to action required of or
inaction by the Company in connection with such registration, except insofar as
the same are caused by or contained in any information furnished in writing to
the Company by such holder expressly for use therein or by such holder's failure
to deliver a copy of the registration statement or prospectus or any amendments
or supplements thereto after the Company has furnished such holder with a
sufficient number of copies of the same. In connection with an underwritten
offering, the Company will indemnify such underwriters, their officers and
directors and each Person who controls such underwriters (within the meaning of
the Securities Act or the Securities Exchange Act) to the same extent as
provided above with respect to the indemnification of the holders of Registrable
Securities.

            (b)   In connection with any registration statement in which a
holder of Registrable Securities is participating, each such holder will furnish
to the Company in writing such information relating to such holder and its
Registrable Securities as the Company reasonably requests for use in connection
with any such registration statement or prospectus and, to the extent permitted
by law, will indemnify the Company, its directors and officers and each Person
who controls the Company (within the meaning of the Securities Act or the
Securities Exchange Act) against any losses, claims, damages, liabilities and
expenses resulting from any untrue or alleged untrue statement of material fact
contained in the registration statement, prospectus or preliminary prospectus or
any amendment thereof or supplement thereto or any omission or alleged omission
of a material fact required to be stated therein or necessary to make the
statements therein not misleading, but only to the extent that such untrue
statement or omission is contained in any information or affidavit so furnished
in writing by such holder which specifically states that it is for use in the
preparation of such registration statement, prospectus or preliminary prospectus
or any amendment thereof or supplement thereto; provided that the obligation to
indemnify will be individual to each holder and will be limited to the net
amount of proceeds received by such holder from the sale of Registrable
Securities pursuant to such registration statement.

            (c)   Any Person entitled to indemnification hereunder will (i) give
prompt written notice to the indemnifying party of any claim with respect to
which it seeks indemnification (but any failure to so notify the indemnifying
party shall not relieve it of any liability which it may otherwise have to any
indemnified party unless such failure shall materially adversely affect the
defense of such

                                        8

<PAGE>

claim) and (ii) unless in such indemnified party's reasonable judgment a
conflict of interest between such indemnified and indemnifying parties may exist
with respect to such claim, permit such indemnifying party to assume the defense
of such claim with counsel reasonably satisfactory to the indemnified party. If
such defense is assumed, the indemnifying party will not be subject to any
liability for any settlement made by the indemnified party without its consent
(but such consent will not be unreasonably withheld). An indemnifying party who
is not entitled to, or elects not to, assume the defense of a claim will not be
obligated to pay the fees and expenses of more than one counsel for all parties
indemnified by such indemnifying party with respect to such claim, unless in the
reasonable judgment of any indemnified party a conflict of interest may exist
between such indemnified party and any other of such indemnified parties with
respect to such claim.

            (d)   The indemnification provided for under this Agreement will
remain in full force and effect regardless of any investigation made by or on
behalf of the indemnified party or any officer, director or controlling Person
of such indemnified party and will survive the transfer of securities. The
Company also agrees to make such provisions, as are reasonably requested by any
indemnified party, for contribution to such party in such proportion as is
appropriate to reflect the relative benefits received by, and the relative fault
of, the Company and such indemnified party in the event the Company's
indemnification is unavailable for any reason. The indemnification and
contribution provided for in this Agreement shall be in addition to, and not in
lieu of, the indemnification and contribution provisions in any underwriting or
similar agreement.

      7.    Participation in Registrations.

            (a)   No Person may participate in any registration hereunder which
is underwritten unless such Person (i) agrees to sell such Person's securities
on the basis provided in any underwriting arrangements approved by the Person or
Persons entitled hereunder to approve such arrangements (including, without
limitation, pursuant to the terms of any over-allotment or "green shoe" option
requested by the managing underwriter(s)) and (ii) completes and executes all
questionnaires, powers of attorney, indemnities, underwriting agreements and
other documents reasonably required under the terms of such underwriting
arrangements.

            (b)   Each Person that is participating in any registration
hereunder agrees that, upon receipt of any notice from the Company of the
happening of any event of the kind described in Section 4(e), such Person will
forthwith discontinue the disposition of its Registrable Securities pursuant to
the registration statement until such Person's receipt of the copies of a
supplemented or amended prospectus as contemplated by Section 4(e).

      8.    Current Public Information. At all times after the Company has
effected a Public Offering, the Company will use commercially reasonable efforts
to file all reports required to be filed by it under the Securities Act and the
Securities Exchange Act and the rules and regulations adopted by the Securities
and Exchange Commission thereunder, and will take such further action as any
holder or holders of Registrable Securities may reasonably request, all to the
extent required to enable such holders to sell Registrable Securities pursuant
to Rule 144 adopted by the Securities and Exchange commission under the
Securities Act (as such rule may be amended from time to time) or any similar
rule or regulation hereafter adopted by the Securities and Exchange Commission.

      9.    Definitions.

                                        9

<PAGE>

            (a)   "COMMON STOCK" means the Company's common stock.

            (b)   "COMPANY" includes any successor to the Company resulting from
any merger, consolidation or other reorganization of or including the Company.

            (c)   "EQUITYHOLDERS AGREEMENT" means the Investor Equityholders
Agreement, of even date herewith, entered into by and among the Company and the
Investors.

            (d)   "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.

            (e)   "PUBLIC OFFERING" means the sale in an underwritten public
offering under the Securities Act of equity securities of the Company.

            (f)   "PUBLIC SALE" means any sale of the Company's common stock to
the public pursuant to an offering registered under the Securities Act or to the
public through a broker, dealer or to a market maker pursuant to the provisions
of Rule 144 adopted under the Securities Act.

            (g)   "REGISTRABLE SECURITIES" means (i) any Common Stock issued in
exchange for Units issued and outstanding as of the date hereof, (ii) any Common
Stock issued in exchange for Units issued upon the exercise of options granted
pursuant to the Emergency Medical Services L.P. Equity Option Plan, (iii) any of
the Company's common stock issued or issuable with respect to the securities
referred to in clause (i) or (ii) by way of a stock dividend or stock split or
in connection with a combination of shares, recapitalization, merger,
consolidation or other reorganization, and (iv) any other shares of the
Company's common stock held by Persons holding securities described in clauses
(i), (ii) or (iii). As to any particular Registrable Securities, such securities
will cease to be Registrable Securities when they have been sold pursuant to a
Public Sale. For purposes of this Agreement, a Person will be deemed to be a
holder of Registrable Securities whenever such Person has the right to acquire
directly or indirectly such Registrable Securities (upon conversion, exchange or
exercise in connection with a transfer of securities or otherwise, but
disregarding any restrictions or limitations upon the exercise of such right),
whether or not such acquisition has actually been effected.

            (h)   "REGISTRATION EXPENSES" has the meaning set forth in Section
5(a).

            (i)   "REORGANIZATION DATE" means the date on which the Company, as
a limited partnership, engages in a merger, consolidation or other
reorganization in which the successor is a corporation and the Units are
exchanged for other equity securities of the Company.

            (j)   "SECURITIES ACT" means the Securities Act of 1933, as amended,
or any similar federal law then in force.

            (k)   "SECURITIES AND EXCHANGE COMMISSION" includes any governmental
body or agency succeeding to the functions thereof.

                                       10

<PAGE>

            (l)   "SECURITIES EXCHANGE ACT" means the Securities Exchange Act of
1934, as amended, or any similar federal law then in force.

            (m)   "UNITS" includes any Units issued or issuable by way of a
dividend or split or in connection with a combination of Units,
recapitalization, merger, consolidation or other reorganization.

Unless otherwise stated, other capitalized terms contained herein have the
meanings set forth in the Equityholders Agreement.

      10.   Miscellaneous.

            (a)   No Inconsistent Agreements. The Company will not hereafter
enter into any agreement with respect to its securities which is inconsistent
with or violates the rights granted to the holders of Registrable Securities in
this Agreement.

            (b)   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.

            (c)   Amendments and Waivers. Except as otherwise provided herein,
the provisions of this Agreement may be amended or waived only upon the prior
written consent of the Company, the Majority Onex Investors and the holders of
at least a majority of the Registrable Securities. 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.

            (d)   Successors and Assigns. All covenants and agreements in this
Agreement by or on behalf of any of the parties hereto will bind and inure to
the benefit of the respective successors and assigns of the parties hereto
whether so expressed or not. In addition, whether or not any express assignment
has been made, the provisions of this Agreement which are for the benefit of
purchasers or holders of Registrable Securities are also for the benefit of, and
enforceable by, any subsequent holder of Registrable Securities who agrees to be
bound by the provisions of this Agreement.

            (e)   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
provisions 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.

                                       11

<PAGE>

            (f)   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 as "Investors" with the consent of the Company
and the Majority Onex Investors, by executing and delivering to the Company a
joinder agreement.

            (g)   Interpretation. In this Agreement, unless a contrary intention
appears, (i) the words "herein," "hereof" and "hereunder" and other words of
similar import refer to this Agreement as a whole and not to any particular
Section or other subdivision, (ii) the words "include," "includes" or
"including" shall be deemed to be followed by the words "without limitation,"
(iii) reference to any Section means such Section hereof, (iv) words of any
gender shall be deemed to include each other gender, and (v) 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.

            (h)   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.

            (i)   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.

            (j)   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.

            (k)   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.

            (l)   Complete Agreement. This Agreement, the documents expressly
referred to herein 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.

            (m)   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

                                       12

<PAGE>

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 Day, shall be deemed to have been 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. Such notices, consents and other communications
will be sent to the parties at the addresses specified for notices in the
Equityholders Agreement or to such other address as the recipient has specified
by prior notice to the other parties.

                            [Signature Pages Follow]

                                       13

<PAGE>

      IN WITNESS WHEREOF, this Registration 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

                   [Signature Page to Registration Agreement]

<PAGE>

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

                        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:

[Signature Page to Registration 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 Registration Agreement]

<PAGE>

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

Dated: __March 11, 2005__

                                    INVESTOR

                                        /s/ Colby Bartlett LLC
                                    -----------------------------
                                    Name: Colby Bartlett LLC
                                            Robert Haft, Manager

       [Signature page (joinder agreement) to the Registration Agreement]

<PAGE>

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

Dated: March 11, 2005__

                                    INVESTOR

                                      /s/ Steven Shulman
                                    -----------------------
                                    Name: Steven Shulman

       [Signature page (joinder agreement) to the Registration Agreement]

<PAGE>

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

                                    INVESTOR

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

                                    Name: Angel L. Iscovich

                 [Signature page to the Registration Agreement]

<PAGE>

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

                                                     INVESTOR

                                                     /s/  Joseph Taylor
                                                     --------------------------
                                                     Name: Joseph Taylor

                 [Signature page to the Registration Agreement]

<PAGE>

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

                                    INVESTOR

                                        /s/ Douglas P. Webster
                                    --------------------------------
                                    Name: Douglas P. Webster

                 [Signature page to the Registration Agreement]

<PAGE>

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

                                              INVESTOR

                                                /s/  Terry R. Meadows
                                              ----------------------------------
                                                   Name: Terry R. Meadows

                 [Signature page to the Registration Agreement]
<PAGE>

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

                                    INVESTOR

                                       /s/ Louis K. Meyer
                                    -----------------------------
                                    Name: Louis K. Meyer

                 [Signature page to the Registration Agreement]

<PAGE>

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

                                    INVESTOR

                                        /s/ James L. Murphy
                                    -------------------------
                                    Name: James L. Murphy

                 [Signature page to the Registration Agreement]

<PAGE>

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

                                    INVESTOR

                                        /s/ Don S. Harvey
                                    --------------------------
                                    Name: Don S. Harvey

                 [Signature page to the Registration Agreement]

<PAGE>

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

                                    INVESTOR

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

                 [Signature page to the Registration Agreement]

<PAGE>

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

                                    INVESTOR

                                        /s/  Dighton Packard
                                    ---------------------------
                                    Name: Dighton Packard

                 [Signature page to the Registration Agreement]

<PAGE>

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

                                    INVESTOR

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

                 [Signature page to the Registration Agreement]
<PAGE>

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

                                    INVESTOR

                                        /s/ David Mintz
                                    -------------------------
                                    Name: David Mintz

                 [Signature page to the Registration Agreement]

<PAGE>

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

                                    INVESTOR

                                      /s/ Steven W. Ratton, Jr.
                                    ---------------------------
                                    Name: Steven W. Ratton, Jr.

                 [Signature page to the Registration Agreement]

<PAGE>

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

                                    INVESTOR

                                        /s/ Randel Owen
                                    --------------------------
                                    Name: Randel Owen

                 [Signature page to the Registration Agreement]

<PAGE>

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

                                    INVESTOR

                                        /s/ Russell Harris MD
                                    -------------------------
                                    Name: Russell Harris M.D.

                 [Signature page to the Registration Agreement]

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

                                    INVESTOR

                                /s/ James T. Kelly
                              --------------------
                              Name: James T. Kelly

                 [Signature page to the Registration Agreement]
<PAGE>
IN WITNESS WHEREOF, this Registration Agreement has been duly executed by the
parties hereto, all as of the date first above written.

                                    INVESTOR

                               /s/ Steven B. Epstein
                             -----------------------
                             Name: Steven B. Epstein

                 [Signature page to the Registration Agreement]

                                        2
<PAGE>
IN WITNESS WHEREOF, this Registration Agreement has been duly executed by the
parties hereto, all as of the date first above written.

                                    INVESTOR

                               /s/ Michael L. Smith
                             ----------------------
                             Name: Michael L. Smith

                 [Signature page to the Registration Agreement]

                                        3

<PAGE>

                                   Schedule A

Onex American Holdings II LLC
Onex US Principals LP
EMS Executive Investco LLC
Onex EMSC Co-Invest LP
Onex Partners LP
Colby Bartlett LLC
Steven J. Shulman
Angel L. Iscovich
Jay Taylor
Terry R. Meadows
Douglas P. Webster
Louis K. Meyer
James L. Murphy
Don S. Harvey
William A. Sanger
Dighton C. Packard
Todd Zimmerman
David Mintz
Steve W. Ratton, Jr.
Randy Owen
Russell H. Harris MD
James T. Kelly
Steven B. Epstein
Michael L. Smith

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