All nine patients with clinical studies leading to positive diagnoses of myocardial infarction had findings on the photoscans suggestive of perfusion defects of the myocardium. In eight of nine photoscans, the sites of the defects correlated well with the locations indicated by the electrocardiograms and coronary arteriograms. Four patients with clinical studies indicating no evidence of myocardial infarction had no findings on the photoscans suggestive of localized perfusion defects. The myocardial photoscan made after injection of cesium chloride Cs 131 appears to be a valuable adjunctive study to evaluate old or recent myocardial infarction.