The available data suggest that the different approaches permit the noninvasive quantification of regional myocardial blood flow in humans with comparable degrees of accuracy. Much of this accuracy depends on how carefully such measurements are performed and on the attention paid to detail when quantitative information is derived from the serially acquired PET images. Although absolute values for estimated flow may differ among laboratories and among techniques, consistency in analysis of data is of utmost importance. Yet, the choice of a specific measurement approach is often determined by practical considerations specific to a given laboratory. Factors are availability of a given tracer, ease of synthesis, proximity of the cyclotron to the scanner, instrument performance, as well as the type of studies performed in the same laboratory in other organs and associated needs for a given tracer. On the other hand, it is clear that the technology for quantifying blood flow in human myocardium has reached a point at which it can be applied routinely and reliably for the study of coronary circulatory physiology and pathophysiology of the human heart. What remains less certain at present is to what extent such quantitative approaches will augment the accuracy with which coronary artery disease can be diagnosed and characterized, and the effects of therapy monitored. However, it is clear that these novel approaches are likely to offer new insights into the pathophysiology of other than apparent coronary artery disease, as exemplified by the initial observations in patients with syndrome-X or hypertrophic cardiomyopathy.(ABSTRACT TRUNCATED AT 250 WORDS)