Positron emission computed tomography is a new technique of potential value for the noninvasive measurement of myocardial blood flow, mechanical function and, in particular, metabolism. The capability of this new study method is attributable to the technologic innovations of the imaging device and the availability of radioactive tracers that are specific for blood flow and metabolism. The device permits recording of cross-sectional images of the left ventricular myocardium that quantitatively reflect regional tracer tissue concentrations. Use of tracer kinetic models with this new technique permits measurements of regional glucose and fatty acid metabolism of the heart. Positron emission tomography is already an important new tool for investigative studies of cardiac physiology and pathophysiology; its clinical utility remains to be defined.