Anterior ST segment depression, found in 13 of 17 patients with acute inferior myocardial infarctions, resolved promptly in all 11 patients whose occluded right coronary arteries were opened with an infusion of streptokinase. Failure of streptokinase to open the artery produced no change in the electrocardiogram. Five of the patients with anterior ST segment depression had normal left anterior descending coronary arteries. In the other patients opening the right coronary artery normalized the anterior ST segments without resulting in collateral flow to the anterior wall, or changing blood pressure or heart rate. Anterior ST depression was a manifestation of the inferior infarction and was not due to anterior ischemia.