The aim of the study was to analyse the type of ECG changes in patients after acute myocardial infarction and to compare them with changes in their physical performance. The authors examined 218 patients with acute myocardial infarction after discharge from hospital. Resting ECG and step-wise graded exercise ECG test on a bicycle ergometer was carried out. The technique of examination was in accordance with WHO recommendations. Statistical evaluation was performed by the Wilcoxon-Mann-Whitney's U-test. The workload in patients showing ECG changes of "transmural" myocardial infarction was not different compared with that of persons with "non-ransmural" lesion (70.00 W versus 71.7 W). When evaluating the relation between the site of ECG changes and the workload, the authors found that the lowest tolerated workload was in cases where ECG changes suggested an extensive damage to the myocardium (53.5 W, p less than 0.05). The authors conclude that the extent of ECG changes after myocardial infarction is a better marker of the level of impairment of physical performance than patient classification to Q or non-Q types.