This clinical study tests the hypothesis that coronary blood flow dynamics of patients may be altered in the immediate interval after a coronary artery bypass procedure which may be deleterious to the patient's future course if unrecognized. Six patients have had complete studies. A thermal dilution catheter is placed into the coronary sinus and threaded to the great anterior vein. Ports are at the tip and more proximal for mixed effluent sampling. Blood samples are used to determine regional oxygen consumption, acid base balance, lactic acid, pyruvate, creatine kinase and lactic dehydrogenase isoenzyme concentrations. Complete hemodynamic evaluations are performed in serial fashion for 6-8 hours after operation. The results to date show wide variation of response to blood flow augmentation. In some, no significant changes in coronary vascular resistance, cardiac output, or any of the biochemical variables occur. Other patients show changes which can be related to less than optimal contractility and systemic flow. One patient demonstrated an increase in coronary vascular resistance prior to a decrease in cardiac output. This was reversed with a calcium channel blocking agent. The project continues.