123I-hexadecenoic acid is a terminally iodinated, 17-carbon fatty acid analog which is rapidly degraded in the myocardium. By determining regional myocardial distribution patterns and clearance rates, it may become useful as a single agent for estimating regional myocardial perfusion and for distinguishing viable ischemic tissue from infarcted tissue. The high count rates obtainable with the I label permit acquisition of qualitative multiprojection images in only 3 min per view or quantifiable single projection high count images in 10 min. Ischemic defects may be observed in anginal patients without subjecting them to stress.