This study was conducted to investigate the functional capacity in postmyocardial infarction. Eighty-four multistage treadmill exercise tests were performed on 60 patients, none of whom had had any formal rehabilitation or regular exercise. There were 50 men and 10 women, ranging in age from 30 to 81 with an average age of 60. The time interval between the acute attack and the exercise test ranged from one month to 9 years. Even though severe infarction affects the exercise capacity for a long time after an acute attack, its effect on cardiac function was more obvious than that on physical capacity. Age was the most important determinant of physical capacity, and the slope of decreasing physical capacity with age in patients with infarct was the same as that in normal subjects. Cardiac function also decreased with age. However, during the early recovery phase, cardiac function was influenced by the severity of infarction and the influence of age could not be established. There was no significant correlation between early ambulation and physical capacity. The beneficial effects of early ambulation may be lost if physical activity is discontinued for some time after the acute attack. The physical capacity increased 2-3 years after the acute attack, but myocardial function did not change significantly.