Positron emission tomography (PET) has been providing new information in the diagnosis and the pathophysiological assessment of heart diseases. The PET tracers commonly used in Japan are 13N-ammonia, 18F-fluorodeoxyglucose (FDG) for imaging of myocardial perfusion and metabolism, respectively. Measurement of regional myocardial blood flow by 13N-ammonia dynamic PET scan and a compartment model analysis is applied to the functional estimation of coronary stenotic lesions and the detection of perfusion abnormalities in hypertrophic heart diseases, familial hyperchlesterolemia and other diseases with possible microvascular lesions. 18F-FDG is commonly used to differentiate ischemic but viable tissue from myocardial scar in coronary artery disease and also used to detect cardiac tumor and the cardiac involvement in sarcoidosis. In addition to these two tracers, 11C-acetate is now expected to provide the clinical analysis of pathophysiology of heart failure by estimating the efficiency of energy conversion of the heart into external work.