The regression of the ECG signs of myocardial infarction has been studied in 101 patients. A significant increase in R wave amplitude and decrease in Q wave depth on the standard ECG was observed over three months. In 21% of the patients, Q waves disappeared completely. In inferior infarction, these changes were more apparent in the lateral V leads than in the inferior limb leads. Patients with intraventricular conduction defects were excluded. Two factors associated with the Q and R wave changes have been identified. Lower heart rates appeared to facilitate the recovery of R waves, and smaller infarcts, as assessed by peak LDH, showed greater ECG recovery. This study raises the interesting possibility that modification of the heart rate may affect favourably the healing process after an acute myocardial infarction.