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                                                                   EXHIBIT 10.19


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


         THIS AMENDMENT to the Operating Agreement of the Company is effective
as of December 1, 1999 (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, 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 Capital Accounts of
                           the Nonguarantor Members in accordance with (b)

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                           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 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 Allocations 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 Allocations 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
                  Account 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 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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