Cardiac transplantation is developing into a routine therapy with widespread availability. Nuclear medicine studies play an important role in evaluating potential transplant recipients and in providing documentation of the severity of ventricular dysfunction and the presence of ischemic but viable myocardium. Nuclear cardiology has increased our knowledge of the physiology of cardiac transplants and is now playing an increasing adjunctive role in management. Radionuclide ventriculography performed early after transplantation can identify patients both with abnormal biventricular function resulting from preservation injury and with isolated right ventricular dysfunction. It also provides important functional data that complements the cardiac biopsy in allograft rejection. New techniques such as 111In antimyosin antibodies and 111In lymphocytes have potential value for the accurate, noninvasive diagnosis of rejection. PET promises to improve the ability to diagnose coronary atherosclerosis of the allograft.