Myocardial infarction is a major cause of mortality worldwide. Physical exercise appears to reduce complications associated with myocardial infarction by contributing to cardiac remodeling. The aim of this study was to investigate the relation between cardiac remodeling and short-term physical activity. We segregated 9 male Wistar rats into 3 groups: non-operated control, sham-operated (subjected to open chest surgery), and operated (subjected to open chest surgery and ligation of the left anterior descending coronary artery). Operated and sham-operated animals were enrolled in a physical activity program shortly after surgical recovery. Non-operated control rats did not receive physical activity stimulation. The heart size and heart wet weight/body weight ratio in operated rats significantly increased compared with that in control or sham-operated rats. Moreover, operated rats showed histological evidence of myocardial cell swelling and disorganization of myocyte architecture. These changes were not observed in control or sham-operated rats. Performing short-term physical activity at the acute phase of myocardial injury does not mitigate the effects of myocardial infarction, as evidenced by increased heart size and altered histological features. Longer training sessions might be required for obtaining any benefit.