This project applies positron emission tomographic (PET) scanning after administration of 6-[18F]fluorodopamine ([18F]-6F-DA) to visualize sympathetic innervation and function in patients with neurocardiologic disorders. Patients undergo infusion of [18F]-6F-DA, followed by PET scanning of one or more body regions. Patients may also undergo PET scanning after administration of [13N]-ammonia, to assess regional perfusion; regional blood sampling (including sampling from the coronary sinus or great cardiac vein) during infusion of [3H]-l-norepinephrine ([3H]-NE), to assess the kinetics and metabolism of NE; or magnetic resonance imaging (MRI) to delineate the ventricular myocardium. PET scanning after [18F]-6F-DA administration, in conjunction with other clinical assessment tools, should provide comprehensive information about regional sympathoneural innervation and function in neurocardiologic disorders.