Exhibit 10.43
Amendment to Employment Agreement between Registrant and Paul Mahon

AMENDMENT

     THIS AMENDMENT is made as of the 11th day of December, 2002 to the
Employment Agreement between Paul A. Mahon (“Executive”) and United Therapeutics
Corporation dated June 16, 2001 (the “Agreement”).

     WHEREAS, the parties desire to amend the Agreement as provided below.

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

     1.     Anti-Moonlighting Provision. Notwithstanding any other provision of
the Agreement to the contrary, the Executive agrees not to “moonlight” in any
manner other than to perform such nominal work with the law firm of Mahon
Patusky Rothblatt & Fisher, Chartered as is consistent with maintaining
professional obligations with respect to the practice of law in the
jurisdictions in which the Executive is licensed or may become licensed.

     2.     Effect. No other provisions of the Agreement shall be affected by
this Amendment, and all other provisions of the Agreement shall remain in full
force and effect.

     In witness whereof, the parties have executed this Amendment effective as
of the date first written above.

  UNITED THERAPEUTICS CORPORATION

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Paul A. Mahon Martine Rothblatt, CEO