The effects of bicycle training for 5 weeks were evaluated in 12 patients after myocardial infarction with left ventricular dysfunction (left ventricular ejection fraction < 40%) and at least one episode of cardiac failure in the past. The patients were divided into two groups of six according to the Weber classification: Group B (VO2/kg/min: 16-20) and Group C (VO2/kg/min: 10-15). Cardiopulmonary and hemodynamic parameters were evaluated during a maximal exercise test and a simultaneous catheterization of the right side of the heart before and after the training. An increase in the capacity for work was recorded in Group B (p < 0.02), while Group C remained unchanged. A statistically significant increase in minute ventilation (p < 0.05) and VO2/kg/min (p < 0.0006) was recorded in Group B. Group C showed an increase in the mean pulmonary arterial pressure (p < 0.03). All of the other parameters remained unchanged after training. We conclude that physical rehabilitation improves the tolerance to exercise in patients with a mildly depressed cardiac function (Group B) but not in patients with a very depressed cardiac function (Group C).