To directly evaluate the effect of physical exercise on survival, 80 rats were randomly assigned to either sedentary life (n = 40) or physical exercise 7 days/week during 6 weeks (n = 40), starting 2 weeks after coronary ligation. All animals were followed daily for 183 days. Size of myocardial infarction was determined by planimetry of serial histologic sections of the left ventricle. Physical exercise had no effect on survival in the total treatment group. However, rats with large myocardial infarctions, randomized to physical exercise, had significantly (p = 0.03) better survival (50%) after 6 months than control rats (17%) with large infarctions.