The effects of intense and prolonged exercise training on the heart were studied with echocardiography in eight men with coronary artery disease with a mean age ( ±standard error of the mean) of 52 ± 3 years. Training consisted of endurance exercise 3 times/week at 50 to 60 percent of the measured maximal oxygen uptake for 3 months followed by exercise 4 to 5 days/week at 70 to 80 percent of maximal oxygen uptake for 9 months. Maximal oxygen uptake capacity increased by 42 percent (26 ± 1 versus 37 ± 2 ml/kg per min; p < 0.001). Heart rate at rest and sub-maximal heart rate and systolic blood pressure at a given work rate were significantly lower after training. Systolic blood pressure at the time of maximal exercise increased (145 ± 9 before versus 166 ± 8 mm Hg after training; probability [p] < 0.01). Left ventricular end-diastolic diameter was increased after 12 months of training (from 47 ± 1 to 51 ± 1 mm; p < 0.01). Left ventricular fractional shortening and mean velocity of circumferential shortening decreased progressively in response to graded isometric handgrip exercise before training but not after training. At comparable levels of blood pressure during static exercise, mean velocity of circumferential shortening was significantly higher after training (0.76 ± 0.04 versus 0.98 ± 0.07 diameter/sec, p < 0.01). No improvement in echocardiographic or exercise variables was observed over a 12 month period in another group of five patients who did not exercise. Thus the data suggest that prolonged and vigorous exercise training in selected patients with coronary artery disease can elicit cardiac adaptations.