Quantitative imaging capabilities, the large number of radiotracers labeled with short-lived positron-emitting isotopes, and appropriate tracer kinetic models offer a broad range of possibilities for probing different aspects of normal and diseased human myocardium. To some extent, PET has already had an impact on clinical cardiology and can decisively influence patient management. At the same time, PET offers tools for elucidating mechanisms of disease and for monitoring responses to treatment. It is also likely to offer new insights into myocardial function in normal and pathologic conditions. Although these insights may initially seem to lack clinical implications, they are likely to lead to a new hypothesis which can simultaneously be tested. The considerable range of assay techniques available with PET is likely to contribute to a more comprehensive characterization of abnormal processes. This, in turn, may lead to new therapeutic opportunities and, thus, result in a broader utilization of PET in cardiovascular disease.