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                                                                   EXHIBIT 10.23

                                  AMENDMENT TO
                             OPERATING AGREEMENT OF
                   HEART HOSPITAL OF DTO, LLC (the "Company")


         THIS AMENDMENT to the Operating Agreement of the Company is effective
as of October 1, 2000 (the "Amendment").

         This Amendment is made under the terms of Section 11.1(e) of the
Operating Agreement 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 Members.

         Accordingly, the Operating Agreement is hereby amended as follows:

         1.       A new Section 5.17 is hereby added to the Operating Agreement
                  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 Members") and such guarantees are not provided on
                  a pro rata basis by all other Members of the Company (the
                  "Nonguarantor Members"), then the Guarantor Members shall be
                  paid an annual guarantee fee equal to (a) the amount of such
                  indebtedness which is guaranteed by the Guarantor Members or
                  its Affiliates, multiplied by (b) .0075, multiplied by (c) the
                  percentage Membership Interest in the Company owned by the
                  Nonguarantor Members (the "Guarantee Fee"). The Guarantee Fee
                  shall be paid quarterly and the expense thereof shall be
                  allocated to the Nonguarantor Members as follows:

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

                                    (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 Members
                           and the amount of such payments shall be charged to
                           the Capital Accounts of the Nonguarantor Members;

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


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                           Capital Accounts of the Nonguarantor Members in
                           accordance with (b) above and any remaining Cash
                           Distributions shall be distributed to the Members 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 amounts then due on loans made by the Members to the
                  Company, shall be distributed quarterly by the Managers as
                  Cash Distributions according to the relative percentage
                  Membership Interests of the Members 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 Members and paid
                  to the Guarantor Members as set forth in Section 5.17.
                  Notwithstanding anything herein to the contrary, no
                  distributions shall be made to Members 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 the
                  Regulatory Allocation Exhibit 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 the
                  Regulatory Allocation Exhibit 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
                  Accounts attributable to the payment by the Company of
                  Guarantee Fees shall be allocated to the Nonguarantor Members
                  in accordance with their relative percentage Membership
                  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 Members or their
                           Affiliates as creditors; and

Except as provided herein, the Operating Agreement 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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