 PURPOSE AND OBJECTIVE: Endogenously produced carbon monoxide CO is known to act as a physiologic signaling molecule to induce mitochondrial biogenesis. This study will test if low-level CO preconditioning induces myocardial biogenesis in humans and if clinical benefit is derived from it. STUDY ACTIVITIES AND POPULATION: The study is an interventional, prospective, randomized, double-blinded trial with a 2-week follow up period. Forty subjects will be recruited from the population of patients scheduled to undergo elective aortic valve replacement. For safety purposes patients with coronary disease will be excluded. Subjects meeting the inclusion criteria will be randomized to receive either air or air containing CO 200ppm as a one-hour inhalational treatment per day over the course of the three days immediately prior to their scheduled operation. Biochemical markers for mitochondrial biogenesis blood and right atrial tissue and clinical outcome parameters BUNcreatinine, and left ventricular function measured by 2D echo will be measured in all patients pre and post-operatively. Right atrial tissue samples will be collected from tissue that is routinely excised during placement of venous cannulas for cardiopulmonary bypass. RISKSAFETY DATA ANALYSIS: Risks will be those of CO inhalation and blood drawing. The 200ppm dose chosen is within OSHA work place exposure limits and has been used safely in human subjects previously. Data will be analyzed by comparing biogenetic marker levels and clinical parameters pre and post intervention and control to CO treatment group. 