Myocardial damage is a frequent complication of cardiac surgery by direct mechanical trauma during the surgical procedure and by myocardial ischemia, which occurs during the cardiopulmonary bypass (CBP). Because the concentrations of biomarkers in the blood collected from the coronary sinus are the best witness of the myocardial damages, we measured the levels of specific cardiac troponin I (c-TnI) and nonspecific (adenosine, myoglobin) markers of left ventricular damages in the coronary sinus of patients during cardiac surgery. Thirty patients who underwent aortic valve replacement for aortic stenosis were included. Blood samples were collected in the coronary sinus and in the radial artery at the beginning (T0), at the end of the CBP (T1), and then 24 hours later (T2). At T0 and T1, adenosine, c-TnI, and myoglobin levels were significantly higher in the coronary sinus than in the radial artery (T0: adenosine: mean +27%; c-TnI: +41%; myoglobin: +28%; T1: adenosine: mean +58%; c-TnI: +58%; myoglobin: +25%; p < .001). These parameters were significantly higher in the coronary sinus at T1 compared with T0 (adenosine: +50%; c-TnI: +229%; myoglobin: +94%; p < .01) and in the radial artery (adenosine: +21%; c-TnI: +194%; myoglobin: +98%; p < .01). At T2, c-TnI further increased. Damages to the myocardium during cardiac surgery are minimal in our surgical conditions but are probably underestimated when using markers measured at the peripheral level. However, most of the damages appear several hours after the surgery.