This study examined the effect of exercise duration on the changes in left ventricular end-diastolic volume in 121 healthy men. The subjects underwent multistage symptom limited upright exercise testing, and terminated the exercise because of excessive fatigue or leg weakness. The subjects were dividend into three groups according to their exercise tolerance: those in group 1 had an exercise duration ≤ 7.5 minutes; in group 2, 7.6-15.0 minutes; and in group 3, >15 minutes. The three groups had a similar increase in end-diastolic volume and also a decrease in end-systolic volume with exercise. The subjects in group 3 were the youngest of any group and had high exercise heart rate and cardiac indexes (P<.01). Similar results were obtained when the subjects were grouped according to their maximum oxygen requirements. A correlation matrix of continuous variables showed that the exercise duration and maximum oxygen requirement are significantly related to age, but not to the changes in left ventricular ejection fraction or end-diastolic volume with exercise. Thus, the Frank-Starling mechanism and increased contractility are to be considered during upright exercise; the exercise duration is not an important determinant of the change in left ventricular end-diastolic volume.