Background Aprotinin is a serine protease inhibitor used extensively in cardiac operations to reduce postoperative bleeding. It also has cardioprotective effects in ischemia/reperfusion injury. In this study, the effects of aprotinin on the release of cardiac markers were evaluated in patients who had good ventricular function and were undergoing coronary artery bypass grafting with cardiopulmonary bypass (CPB). Methods and Results Eighty male patients with an ejection fraction ≥40%, were randomized into either an aprotinin (Group-I; n=40) or control (Group-II; n=40) group. Patients in the aprotinin group received the full Hammersmith doses of aprotinin (2×10⁶ KIU pre-CPB, 2×10⁶ KIU at pump prime, 500,000 KIU/h during CPB), whereas the patients in the control group received only saline solutions. Cardiac troponin-I (cTnI) levels were measured before surgery, immediately after surgery, and at postoperative 6^th, 12^th, 24^th h and 5^th day. Creatine kinase (CK)-MB measurements were performed at the same time except for the postoperative 5^th day. Cardiac index (CI), mixed venous oxygen saturation and lactate dehydrogenase (LDH) measurements were also performed. Conclusion Although all patients were in reasonable condition, less myocardial enzyme leakage occurred on the aprotinin group, suggesting that aprotinin has a protective effect on the myocardium beyond that achieved with blood cardioplegia and systemic hypothermia. Because of aprotinin's effects on multiple targets of metabolism, its protective value might increase in more complicated cases. (Circ J 2006; 70: 1432 - 1436)