Cardiac imaging is extremely important because of the high prevalence and morbidity of cardiovascular disease. Single-photon emission computed tomography (SPECT) and positron emission tomography (PET) have been the methods of choice for imaging myocardial perfusion. Myocardial perfusion imaging is probably almost as relevant as the morphologic depiction of the coronaries, because a morphological stenosis does not necessarily result in distal myocardial hypoperfusion, as collateralization may be present. Thus, treatment of a morphologic coronary abnormality always requires unequivocal proof that ischemia is present in the patient, whether on the basis of clear clinical signs and symptoms or perfusion imaging.