In order to evaluate the left ventricular performance during exercise in patients with myocardial infarction, we performed a symptom-limited multistage exercise test using a bicycle ergometer in the supine position on 82 patients with myocardial infarction, and their hemodynamic responses to exercise were analyzed. Patients were subdivided into three groups according to the levels of pulmonary capillary wedge pressure (PCWP) and cardiac index (CI) obtained at the end-point of the exercise: Group I (20 patients) with PCWP<18 mmHg and CI&ges;5.0 L/min/m² ; Group II (32 patients) with PCWP&ges;18 mmHg and CI&ges;5.0 L/min/m² ; Group III (30 patients) with PCWP&ges;18 mmHg and CI<5.0 L/min/m² . Exercise tolerance expressed as the duration of exercise was 11.9±0.5 (SEM) min in Group I, 10.6±0.4 in Group II and 7.8±0.5 in Group III, which was closely correlated with the left ventricular function observed at the end-point of the exercise. During exercise stroke volume index (SVI) decreased slightly in Group III, while it increased significantly in Groups I and II. The extent of coronary artery lesion in Group III was more severe than in Groups I and II. In 50 patients without prior myocardial infarction, infarct size estimated by total released CPK was larger in Group III than in Group I. These findings indicate that coronary artery lesion and infarct size are important factors contributing to left ventricular performance during exercise in patients with myocardial infarction.