Positron-emission tomography is an advanced imaging technology that can be used for the noninvasive evaluation of myocardial blood flow, determination of myocardial metabolism, and the assessment of myocardial tissue viability. 82Rb and 13N-ammonia represent the most commonly used tracers for qualitative evaluation of regional myocardial perfusion. In combination with pharmacologic vasodilation, these agents provide accurate detection of coronary artery disease. Comparative studies using single-photon emission CT with 201Tl have shown 82Rb positron-emission tomography to be superior in terms of diagnostic accuracy. The use of tracer kinetic modeling with the radiopharmaceuticals 15O-water or 13N-ammonia has allowed accurate quantification of myocardial blood flow and determination of regional coronary flow reserve using dynamic positron-emission tomography imaging. The labeling of metabolic substrates such as 11C-palmitate, 11C-acetate, and 18F-fluorodeoxyglucose has proven to be useful in evaluating cardiac metabolism. The use of fluorodeoxyglucose uptake as a marker of exogenous myocardial glucose utilization allows the differentiation of ischemic but viable tissue from myocardial scar. The relationship of 11C-acetate turnover to oxidative metabolism and myocardial oxygen consumption may have important future applications for evaluating the efficiency of energy conversion of the heart into external work. Such a parameter could be used to evaluate the condition of patients with impaired left ventricular performance and to assess their response to therapy. Positron-emission tomography offers a useful research and clinical tool for the noninvasive evaluation of many aspects of cardiac disease. With the development of quantitative techniques, the clinical importance of positron-emission tomography is expected to further increase in the future.