The presence of an abnormal P terminal force of the P wave in lead V1 (PTFV1) was demonstrated on the initial electrocardiograms in 69 of the 200 patients with transmural acute myocardial infarction. 61.5% of the total cases with a lethal outcome during hospitalization belonged to this group. The mortality of the patients who presented this ECG sign of left atrial hypertension at the onset was 53.7%, thus differing significantly from that in patients without the sign (22.1%). The PTFV1 anomaly has a prognostic value in patients without complications as well as in those with heart failure at the onset of the disease. The appearance during hospitalization of major arrhythmias and disturbances of conduction and of sudden death is significantly correlated to the presence of abnormal PTFV1 on the admission electrocardiograms.