To determine the effects of exercise training on left ventricular performance and myocardial perfusion in coronary artery disease, rest and exercise radionuclide angiocardiography and thallium-201 scintigraphy were performed before and after 12 weeks of training in 16 coronary patients. After training, 15 of the 16 patients had improved exercise tolerance; total treadmill exercise duration increased from (mean +/- standard error of the mean) 491 +/- 37 to 602 +/- 31 seconds (p less than 0.01), and the estimated rate of oxygen consumption (VO2 max) increased from 29.4 +/- 1.4 to 33.8 +/- 1.2 ml/kg per min (p less than 0.001). Resting left ventricular ejection fraction increased from 52 +/- 4 to 57 +/- 4 percent (p less than 0.02); no change occurred in left ventricular functional reserve assessed by ejection fraction and regional wall motion response to exercise at the same rate-pressure product before and after training. Myocardial perfusion at equivalent pre- and post-training cardiac work loads during exercise and on redistribution was unchanged by training. It is concluded that in patients with coronary heart disease, physical training increases exercise tolerance, and results in minimal improvement in resting left ventricular systolic performance. Functional reserve of both left ventricular systolic performance and the coronary circulation appears to be unchanged by exercise training. These data suggest that the beneficial effects of training for 12 weeks in patients with coronary artery disease predominantly result from factors other than improvement in left ventricular pump performance or perfusion.