Three hundred ninety patients who had successful coronary angioplasty were studied by treadmill exercise testing to determine the incidence and prognostic importance of silent and symptomatic myocardial ischemia in this patient subset. All patients were followed for an average of 11 months. During exercise, 81 patients (20%) had abnormal exercise-induced ST-segment depression without chest pain (group 1). Twenty patients (5%) had chest pain without ST changes (group 2). Twenty-one patients (5%) had both exercise-induced chest pain and ST-T-segment depression (group 3) and 268 patients (70%) had a normal exercise test with no chest pain (group 4). The groups were similar with respect to age, sex, history of previous myocardial infarct and previous coronary bypass surgery. Group 4 included more patients with complete revascularization. Mutually exclusive cardiac events were defined as cardiac death, nonfatal myocardial infarction, class III angina and additional revascularization (coronary angioplasty, coronary artery bypass surgery). The cardiac event rate in groups 1, 2 and 3 were significantly higher than in group 4 (40, 45 and 43 vs 22%; p = 0.001). There were 4 cardiac deaths and 4 nonfatal myocardial infarctions in group 1 compared to 2 cardiac deaths and 3 nonfatal myocardial infarctions in group 4 (p = 0.03 and 0.05, respectively). The event rates in groups 1, 2 and 3 patients with multivessel disease were significantly greater than in group 4 (44, 60 and 47 vs 22%; p = 0.002). Thus, exercise-induced myocardial ischemic episodes, both symptomatic and silent, early after coronary angioplasty are predictive of an unfavorable prognosis and serious cardiac events, particularly in patients with multivessel disease and incomplete revascularization.