ST-segment elevations in the right ventricular lead and those greater in lead III than in lead II strongly suggest that right, rather than left circumflex, coronary arterial occlusion occurs in acute myocardial infarction in the inferior wall. Our study demonstrated that, in the very early stages of infarction, a T-wave amplitude that is greater in lead III than in lead II and an upright or positive biphasic T wave in lead V(5)R are just as predictive as ST-segment changes and are often easier to measure.