CONVERTIBLE PROMISSORY NOTE AMENDMENT NO. 1

Exhibit 10.4

Convertible Promissory Note Amendment No. 1

This Convertible Promissory Note Amendment No. 1 (the “First Amendment to Note”) is entered into as of June 12, 2007 (the “Amendment Date”) by and between PTC Therapeutics, Inc., a Delaware corporation (“PTC”), and CV Therapeutics, Inc., a Delaware corporation (“CVT”), for the purpose of amending the Convertible Promissory Note between the same parties dated June 7, 2006 (hereinafter referred to as the “Convertible Note”), with reference to the following facts and circumstances.

WHEREAS, PTC and CVT entered into the Convertible Note in connection with the Collaboration and License Agreement (the “Collaboration Agreement”) dated as of June 7 ^th , 2006; and

WHEREAS, the parties now wish to amend the terms of Convertible Note as set forth in this First Amendment to Note;

NOW, THEREFORE, IN consideration of the mutual covenants and conditions contained herein, and for other good and valuable consideration, the receipt and adequacy of which are hereby acknowledged, the Parties hereby