After myocardial infarction, ECG may not be abnormal forever. After myocardial infarction occurs, ECG will have specific manifestations, ST segment elevation, and then gradually fall back, T wave inversion, and then the formation of pathologic Q wave, usually in the late stage of myocardial infarction, there will remain the existence of pathologic Q wave, and the ECG examination can be detected abnormalities. However, the ECG may return to normal after infarction. For example, in myocardial infarction, the scope of necrotic myocardium is small, which is common in lower wall myocardial infarction. If the scope of infarction is small and the condition is recovered, sometimes the ECG does not have pathologic Q-wave formation, and the ECG may return to normal. If the scope of myocardial infarction is large, for example, large anterior wall myocardial infarction, Q waves are often left in the anterior wall leads, in which case the ECG may never return to normal.