Exhibit 10.13

ASSIGNMENT

This Assignment, dated as of December 20, 2005, by and among EMCS, Inc. (f/k/a
Emergency Medical Services Corporation), a Delaware corporation (“EMSC”),
Emergency Medical Services L.P., a Delaware limited partnership (“EMS LP”), AMR
HoldCo, Inc., a Delaware corporation (“AMR HoldCo” and, together with EMSC and
EMS LP, the “Purchasers”) and ClaimCo LP, a Delaware limited partnership
(“ClaimCo”).

Reference is made to the Stock Purchase Agreement, dated as of December 6, 2004,
by and among Laidlaw Medical Holdings, Inc., Laidlaw International, Inc.
(together “Laidlaw”) and Purchaser with respect to the purchase of the
outstanding capital stock of American Medical Response, Inc. (the “Purchase
Agreement”). Capitalized terms used herein and not defined shall have the
meaning given to such terms in the Purchase Agreement.

EMS and Laidlaw have had discussions concerning (i) the understatement of
accounts receivable allowances reflected in various balance sheets included in
the historical financial statements of American Medical Response, Inc.,
including an approximately $50 million understatement of such allowances in the
Closing Balance Sheet delivered by Laidlaw to EMS pursuant to Section 1.05 of
the Purchase Agreement and (ii) the claims that may arise under the Purchase
Agreement as a result of such understatements, including, without limitation, a
possible Post-Closing Adjustment under Section 1.05 of the Purchase Agreement
and potential claims for indemnification under Article VIII of the Purchase
Agreement (collectively, the “A/R-Related Claims”).

As permitted by Section 10.03 of the Purchase Agreement, and subject to the
provisions of paragraphs 2 and 3 of this Assignment, Purchasers wish to assign
to ClaimCo, and ClaimCo wishes to accept and assume from Purchasers, Purchasers’
rights under the Purchase Agreement with respect to the A/R-Related Claims (the
“Assigned Rights”).

NOW THEREFORE, intending to be legally bound, the parties hereby agree as
follows:

1. Assignment by Purchasers. Subject to the provisions of paragraphs 2 and 3,
Purchasers hereby assign, transfer, grant and otherwise convey to ClaimCo, and
ClaimCo hereby accepts and assumes from Purchasers, the Assigned Rights.

2. Retained Rights. The Assigned Rights are limited to aggregate recoveries of
ClaimCo, less all costs and expenses incurred by ClaimCo in connection with the
A/R-Related Claims (including, without limitation, costs and expenses of
investigation, attorneys’ fees and expenses and fees and expenses of any other
third parties), totaling $50.0 million, and any recoveries in excess of such
amount shall be and remain the joint property of EMS LP and AMR HoldCo.
Purchasers shall not be responsible for, and shall not fund, any costs or
expenses incurred in connection with the A/R-Related Claims from and after the
effective time of this Assignment.

3. Retained Liability. EMSC acknowledges that it continues to be liable for all
of the obligations of Purchaser under the Purchase Agreement.

*         *         *

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This Assignment shall be deemed to be effective concurrently with the
consummation of the initial public offering of common stock by Emergency Medical
Services Corporation which is being effected on the date hereof.

IN WITNESS WHEREOF, the parties hereto have caused this Assignment to be
executed and delivered as of the date first written above.

 

EMSC, Inc. By:   /s/ Todd G. Zimmerman   Name:   Todd G. Zimmerman   Title:  
Secretary EMERGENCY MEDICAL SERVICES L.P. By:   EMSC, Inc.   its general partner
By:   /s/ Todd G. Zimmerman   Name:   Todd G. Zimmerman   Title:   Secretary AMR
HOLDCO, INC. By:   /s/ Todd G. Zimmerman   Name:   Todd G. Zimmerman   Title:  
Secretary

CLAIMCO LP

By:   EMSC, Inc.   its general partner By:   /s/ Todd G. Zimmerman   Name:  
Todd G. Zimmerman   Title:   Secretary

 

[Signature Page to Assignment]