After intravenous administration of contrast agent, in vitro cardiac scanning showed a significant difference between the attenuation coefficients of the intracavitary blood pool and the myocardial wall, permitting clear delineation of the ventricular cavity. A substantial alteration in hematocrit permitted similar visualization of the intracavitary blood pool-myocardial wall interface. The attenuation coefficient of infarcted myocardium differed sufficiently from that of normal myocardium to render computed tomographic distinction feasible. In three hour old infarctions, the differences between normal and ischemic or infarcted tissue were enhanced by prior administration of contrast agent. These differences in attenuation coefficient indicate that a properly gated CT scanner could be utilized as a noninvasive approach to evaluating suspected or known myocardial infarction and other aspects of cardiac structure and function both in man and in experimental animals.