 This study will test if inhalation of Carbon Monoxide CO will increase the numbers of mitochondria in heart muscle. Mitochondria are the small components of muscle and other cells that convert fuel and oxygen to the easily usable forms of energy ATP that power all cells activities. Adequate numbers of healthy mitochondria are essential to heart cell function. From animal and other studies we have reason to believe that breathing small amounts of CO will signal the body to increase the numbers of mitochondria in heart cells. We propose to test this theory in heart valve surgery patients by examining a small sample of heart tissue from the right atrial appendage that is routinely cut out during the preparation of the patient for cardio-pulmonary bypass and that would otherwise be discarded by the surgeon. Muscle samples from two groups of subjects will be compared. One group will breath CO and the other group will breath room air. If CO is effective, we should notice an increase in the numbers of mitochondria in the group that was exposed to CO compared to the group that breathed room air. 