To determine whether endurance exercise training can improve left ventricular systolic function in older men, 10 healthy sedentary men (64 +/- 3 years old; mean +/- SD) were studied. Training consisted of endurance exercise 4 +/- 0.3 days per week for 11.8 +/- 2.5 months at a progressively increasing intensity of 60-80% of maximal O2 uptake (Vo2max) with additional brief bouts of exercise equal to 93 +/- 13% of Vo2max. Vo2max increased from 29.6 +/- 4.1 to 37.2 +/- 5.7 ml/kg/min (p less than 0.001). Percent body fat was decreased (17.8 +/- 3.6% versus 15.6 +/- 3.6%; p less than 0.001). Before training, left ventricular ejection fraction, determined by electrocardiographic-gated equilibrium blood pool imaging, increased only modestly during exercise (from 66.3 +/- 6.7% at rest to 70.6 +/- 6.9% at peak exercise). After training, the increase in ejection fraction during exercise was significantly greater (from 67 +/- 4.8% at rest to 77.6 +/- 7.5% at peak exercise) than that observed before training and was similar to that in young sedentary men (64 +/- 7% at rest versus 74 +/- 9% at peak exercise). Although the changes in systolic pressure from rest to exercise were similar, end-systolic volume decreased significantly at peak exercise after (51 +/- 12 versus 38 +/- 13 ml; p less than 0.005) but not before (46 +/- 8 versus 43 +/- 13 ml; p = NS) training with a shift in the end-systolic volume-systolic blood pressure relation to the left compatible with enhanced inotropic state.(ABSTRACT TRUNCATED AT 250 WORDS)