In contrast to ST-segment depression during exercise, the mechanism for ST-segment elevation - a more unusual finding - is controversial and poorly understood. Exercise induced ST-segment elevation of 2 mm and more was observed in 80 of 3000 consecutive patients (2.6%) undergoing bicycle exercise testing using 6 of 12 ECG leads. This abnormality was detected in 70 of 777 patients (9%) with documented previous myocardial infarction and in 10 of 2223 (0.5%) patients without a history of myocardial necrosis and with normal resting ECG. The substantial differences in exercise induced ST-segment elevation between these two groups are: patients with previous myocardial infarction and angiographically documented left ventricular aneurysm revealed progressive asymptomatic ST-segment elevation on an average of 3.4 +/- 1.2 mm persisting for a long time (greater than 3 minutes) during the recovery period. The extent of ST-segment elevation appears to correlate with LV EF and LV volume. These patients should be treated medically (as in 73% of our patients), and cardiac catheterization is indicated only in the presence of severe angina, congestive LV failure and arrhythmias. Patients with normal ECG at rest showed ST-elevation at maximal exercise. ST-segment elevation was associated with chest pain, which was more pronounced and shorter in duration than in the other group (9.1 +/- 2.8 mm, less than 30 sec). ST-elevation was abrupt and not preceded by ST-segment depression. 8 of 10 patients with anterior ST-segment elevation had a left anterior descending artery (LAD) lesion. Therefore, exercise testing in this group predicts significant proximal LAD obstruction accessible for PTCA.