The incidence of ischemic myocardial injury was ascertained in 43 patients undergoing combined aortic valve replacement (AVR) and coronary artery bypass grafts (CABG) and compared with the incidence in patients with only AVR or CABG. Correlation was made with aortic cross-clamp time, cross-clamp and fibrillation time, and left ventricular biopsy. Myocardial infarction occurred in 21% (nine of 44) of AVR and CABG patients, 7% (eight of 119) of AVR patients, and 14% (16 of 112) of CABG patients. All patients with aortic cross-clamp times greater than 70 minutes or fibrillation times greater than two hours in the AVR and CABG group had myocardial injury. The hypertrophied ventricle is more susceptible to ischemic damage because of subendocardial hypoperfusion, especially in the fibrillating heart during reperfusion. Cross-clamp times greater than 70 minutes and fibrillation times greater than two hours should be avoided in AVR and CABG patients.