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Changes in left ventricular (LV) volumes and ejection fraction between rest and maximal supine exercise were evaluated in 11 patients who had had four epicardial markers placed during coronary artery surgery. After calibrating marker distances with respect to volume (r = 0.92--0.99) over one cardiac cycle for each patient, regression equations were used to compute LV volume from marker measurements for beats before and during exercise. The response of the left ventricle to exercise and the extent of revascularization could not be predicted from resting LV volume or ejection fraction. Ten patients had normal resting end-diastolic volumes and eight had normal resting ejection fractions. With exercise, three had a rise in end-diastolic volume and four had a fall in ejection fraction. Graft patency was greater in the group with an unchanged or increased ejection fraction (86 vs 50%, P less than 0.05). Epicardial clip motion can be used to determine LV volumes and ejection fraction during supine maximal exercise in man. The revascularized ventricle with normal or nearly normal performance in studies done at rest responds by decreasing end-diastolic and end-systolic volume and by increasing the ejection fraction. Increases in volumes or decreases in ejection fraction reflect old myocardial damage from infarction, fibrosis or ischemia from incomplete revascularization.