The distribution of 99mTc-glucoheptonate in normal mice and its accumulation in acutely infarcted myocardium were studied in animals. Rapid blood clearance and low concentration of the tracer in normal myocardium were found in tissue distribution studies performed in mice. Experimental myocardial infarction was performed in nine dogs. Four hours after the intravenous injection of 99mTc-glucoheptonate the uptake ratio of the myocardial infarcted area to normal myocardium was 20:1; to blood, 9:1; and to lung, 6:1. The greatest concentration of radiopharmaceutical in the infarcted tissue was noted in areas that had 20-40% of normal perfusion. Regions of infarction were clearly defined by external gamma scintigraphy. Clinical investigation of this tracer in humans appears warranted.