The appearance of ST segment depression in the exercise ECG serves as a threshold criterion when it comes to determining the "loadability" of myocardial infarction patients carrying out sports activities. In 27 MI patients, the question was investigated as to the extent to which abnormalities taking the form of silent ischemic episodes could be found during cross-country skiing on plains or during downhill skiing at an altitude of 800 to 2,000 meters. Such silent ischemic attacks were found in 20 out of the 27 patients. Both the duration and incidence were higher during sports activities than during normal day-to-day activities. The heart rate at the time of the appearance of the ischemic episodes was lower in the 12-hour ECG than during ergometry. During sports activities, however, the heart rates were frequently higher than the given training pulse rates. Treatment with nitrates (Isoket retard 120 mg) reduced the incidence and duration of silent ischemias. On account of the spontaneous variability of the parameter, it needs to be interpreted with caution. The incidence of silent ischemic episodes during sports activities in patients with clinical anomalies should prompt a rigorous treatment with drugs, and careful supervision of training.