Left ventricular performance was studied before and late (mean 12-17 months) after aortocoronary artery bypass surgery by quantitative, computer-based videoangiography. We measured total function (left ventricular ejection fraction, volumes and end-diastolic pressure) at rest (in 60 patients) and before and after exercise (abnormal exercise hemodynamics preoperatively in 32 patients) and regional function (peak rate of systolic wall thickening) at rest (in 60 patients) and before and after administration of nitroglycerin (in 19 patients). Total left ventricular function at rest is usually unchanged postoperatively. Exercise hemodynamics are more sensitive indexes of performance and, if abnormal, usually improve postoperatively if revascularization has been complete and extensive myocardial infarction has not occurred. Regional myocardial function usually improves postoperatively if the bypass graft to the region is patent and has a blood flow of more than 60 ml/min (measured late postoperatively by videodensitometry) and if no previous infarction was present in the region. Myocardial infarction and graft blood flow of 40 ml/min or less are the two main factors that prevent improvement in abnormal regions defined by the regional wall thickening method when bypass grafts are patent. Regions supplied by occluded grafts show decreases in regional function. The preoperative wall-thickening response to administration of nitroglycerin can be used to distinguish ischemia and significant myocardial infarction and to predict the successful response to aortocoronary bypass graft surgery.