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                                                                   EXHIBIT 10.13
                               FIFTH AMENDMENT TO
                        AGREEMENT OF LIMITED PARTNERSHIP
                                       OF
                             HEART HOSPITAL IV, L.P.

         THIS FIFTH AMENDMENT (the "Amendment") is effective as of the 31st day
of December, 1997 and is entered into by and among HEART HOSPITAL IV, L.P., a
Texas limited partnership (the "Partnership"), HOSPITAL MANAGEMENT IV, INC., a
North Carolina corporation which is the general partner of the Partnership
("HM") and each of the undersigned parties (the "Limited Partners").

                                    RECITALS:

         1.       Prior to the date hereof, the parties hereto have entered into
and become a party to the Agreement of Limited Partnership of the Partnership
dated as of February 22, 1996 (as amended from time to time, in the "Partnership
Agreement");

         2.       The parties desire to further amend the Partnership Agreement
in accordance with the terms of this Amendment;

         NOW, THEREFORE, for good and valuable consideration, the receipt and
sufficiency of which is hereby acknowledged, the parties hereto agree as
follows:

         1.       All defined terms set forth in the Partnership Agreement shall
have the same meaning in this Amendment except as otherwise provided herein.

         2.       Section 5.2(i) of the Partnership Agreement is hereby amended
to delete the phrase "payable by Medicare or Medicaid".

         3.       Section 5.6(b)(ii) of the Partnership Agreement is hereby
amended to add the following provision at the end thereof:

                  The parties acknowledge and agree that the Management Fee paid
                  to HM has been set in advance, is consistent with the fair
                  market value in an arm's-length transaction for the management
                  services, and has not been determined in any manner that takes
                  into account the volume or value of any referrals or business
                  otherwise generated among the Partnership, HM and/or the
                  Investor Partners.

         4.       The following new Section 11.4 is hereby added to the
Partnership Agreement:

                  11.4 Amendments and Modifications to Article V. The Parties
                  acknowledge and agree that if the provisions set forth in
                  Article V of this Agreement are terminated or the compensation
                  provisions are modified, no other agreement, for same or
                  similar items and/or services provided under

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                  this Agreement, may be executed between the Parties until the
                  next anniversary date of such termination or modification,
                  except for the sole purpose of adopting modifications as
                  required by law or recommended by counsel to further legal
                  compliance.

         5.       Except as expressly provided herein, the Partnership Agreement
remains in full force and effect.

         6.       This Amendment may be executed in any number of separate
counterparts, each of which shall be deemed to be original, and the several
counterparts taken together shall constitute the binding agreement of the
parties hereto.

         7.       This Amendment will be effective once it has been executed by
Partners holding, in the aggregate, the percentage of Partnership Interests
necessary to amend the Agreement, as set forth in the Partnership Agreement.

         IN WITNESS WHEREOF, the parties hereto have executed this Amendment as
of the day and year first above written.

[***]

[***] These portions of this exhibit have been omitted and filed separately
      with the Commission pursuant to a request for confidential treatment.

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                                                                  EXHIBIT 10.14
                                  AMENDMENT TO
                       AGREEMENT OF LIMITED PARTNERSHIP OF
                     HEART HOSPITAL IV, L.P. (the "Company")

         THIS AMENDMENT to the Agreement of Limited Partnership of the Company
is effective as of July 31, 2000 (the "Amendment").

         This Amendment is made under the terms of Section 11.1(e) of the
Agreement of Limited Partnership in order to ensure that the Company remains in
compliance with all federal and state laws, rules, regulations and
interpretations thereof. The undersigned have also determined that this
Amendment will not materially reduce the economic return on investment in the
Company to any of its Partners.

         Accordingly, the Agreement of Limited Partnership is hereby amended as
follows:

         1.       A new Section 5.17 is hereby added to the Agreement of Limited
                  Partnership as follows:

                           SECTION 5.17 Guarantee Fee. In the event that any
                  Member of the Company or its Affiliates provide a guarantee of
                  any indebtedness of the Company which is acceptable to and
                  required by the Company's lenders ("Guarantor Partners") and
                  such guarantees are not provided on a pro rata basis by all
                  other Partners of the Company (the "Nonguarantor Partners"),
                  then the Guarantor Partners shall be paid an annual guarantee
                  fee equal to (a) the amount of such indebtedness which is
                  guaranteed by the Guarantor Partners or its Affiliates,
                  multiplied by (b) .0075, multiplied by (c) the percentage
                  Partnership Interest in the Company owned by the Nonguarantor
                  Partners (the "Guarantee Fee"). The Guarantee Fee shall be
                  paid quarterly and the expense thereof shall be allocated to
                  the Nonguarantor Partners as follows:

                                    (a)      The Guarantee Fee shall be deducted
                           from the Cash Distributions otherwise distributable
                           to the Nonguarantor Partners and shall be paid to the
                           Guarantor Partners;

                                    (b)      To the extent that at the time such
                           Guarantee Fee is due to be paid hereunder there are
                           no anticipated Cash Distributions, then the Company
                           shall pay such Guarantee Fee to the Guarantor
                           Partners and the amount of such payments shall be
                           charged to the Capital Accounts of the Nonguarantor
                           Partners;

                                    (c)      When Cash Distributions become
                           available for distribution to the Partners in the
                           future, the Cash Distributions otherwise
                           distributable to the Nonguarantor Partners shall
                           first be retained by the Company to the extent that
                           amounts were previously charged to the Capital
                           Accounts of

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                           the Nonguarantor Partners in accordance with (b)
                           above and any remaining Cash Distributions shall be
                           distributed to the Partners in accordance with
                           Section 6.1.

         2.       Section 6.1 shall be deleted in its entirety and the following
                  new Section 6.1 shall be substituted in lieu thereof:

                           SECTION 6.1 Distributions of Cash Flow from
                  Operations and Cash from Sales or Refinancing. Prior to the
                  dissolution of the Company, Cash Flow from Operations and Cash
                  from Sales or Refinancing, if any, remaining after repayment
                  of any loans made by the Partners to the Company, shall be
                  distributed quarterly by the Managers as Cash Distributions
                  according to the relative percentage Partnership Interests of
                  the Partners and Economic Interest Owners; provided, however,
                  that to the extent possible, any Guarantee Fee shall be
                  deducted from the Cash Distributions otherwise distributable
                  to the Nonguarantor Partners and paid to the Guarantor
                  Partners as set forth in Section 5.17. Notwithstanding
                  anything herein to the contrary, no distributions shall be
                  made to Partners if prohibited by the Act.

         3.       The opening phrase of Section 6.2 shall be deleted and the
                  following shall be substituted in lieu thereof:

                           SECTION 6.2 Profits. Except as provided in Schedule B
                  and subject to Section 6.6, Profits shall be allocated as
                  follows:

         4.       The opening phrase of Section 6.3 shall be deleted and the
                  following shall be substituted in lieu thereof:

                           SECTION 6.3 Losses. Except as provided in Schedule B
                  and subject to Section 6.6, Losses shall be allocated as
                  follows:

         5.       The following shall be added as a new Section 6.6:

                           SECTION 6.6. Special Allocations of Guarantee Fees.
                  Any and all deductions, losses or reductions to Capital
                  Account attributable to the payment by the Company of
                  Guarantee Fees shall be allocated to the Nonguarantor Partners
                  in accordance with their relative percentage Partnership
                  Interests.

         6.       Section 7.3(b)(ii) shall be deleted in its entirety and the
                  following new section shall be substituted in lieu thereof:

                                     (ii)     To the payment of all debts and
                           liabilities (including interest), and further
                           including without limitation any accrued but unpaid
                           Guarantee Fees, owed to the Partners or their
                           Affiliates as creditors; and

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         Except as provided herein, the Agreement of Limited Partnership shall
remain in full force and effect.

[***]

[***] These portions of this exhibit have been omitted and filed separately
      with the Commission pursuant to a request for confidential treatment.

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