The response of left ventricular function during exercise and recovery after exercise was assessed in 52 patients with coronary artery bypass surgery by means of a radionuclide continuous ventricular function monitor. This system consists of 2 radionuclide detectors, recorder and a computer. After the equilibration of 20 mCi technetium 99m-labeled autologaous red blood cells into the intravascular space, the beat by beat radionuclide data were summed for 20-sec intervals to measure left ventricular ejection fraction (EF). Before surgery, the mean EF decreased with exercise from 51 +/- 9% to 45 +/- 11% (p less than 0.001). Cardiac response was divided into 4 types according to the profiles of the EFs during exercise. In 6 patients, EF continued to increase until maximal exercise (type A). In 10 patients, EF initially increased and then decreased in late exercise stages (type B). In 9 patients, EF did not change significantly during exercise (type C). In 27 patients, EF decreased throughout exercise (type D). After surgery, the mean EF increased with exercise from 53 +/- 10% to 60 +/- 13% (p less than 0.001). Thirty-five patients showed type A, 9 type B, 5 type C, and 3 type D. Two type D and 5 type B patients had occluded grafts or ungrafted coronary arteries. Four patients with complete revascularization including an internal thoracic artery and saphenous vein grafts showed type B. Three patients with extensive infarction and poor left ventricular function showed type C.(ABSTRACT TRUNCATED AT 250 WORDS)