Nuclear cardiology, and in particular myocardial scintigraphy, is used with increasing frequency to detect the presence of ischemia before revascularization by angioplasty or coronary artery bypass grafting. On the basis of recent publications it is evident that there are certain conditions in which conventional diagnostic methods suggest the presence of myocardial necrosis, but there is persistent metabolically active myocardial tissue. One of these conditions is the "hibernating myocardium". Patients with this disease entity will show an improvement in cardiac function after revascularization in over 85% cases. Therefore, the diagnosis of "hibernating myocardium" has a high predictive value. Differentiation between irreversible myocardial necrosis and "hibernating myocardium" is possible by positron emission tomography (PET) combining imaging of myocardial metabolism with imaging of myocardial perfusion. With 30 months, 36 patients with established myocardial infarction and a suspicion of "hibernating myocardium" have been examined in the PET scanner at the Paul Scherrer Institute, Villigen. Images of glucose metabolism were obtained by 18-fluoro-deoxyglucose and perfusion images were obtained using thallium in a first phase (thallium-SPECT at rest) and rubidium-82) as a positron emitter in second phase. We were able to identify patterns that suggest the presence of "hibernating myocardium", in 19 of 36 patients (53%). The basic principles and limitations of myocardial positron emission tomography are discussed.