Clinical and autopsy studies have consistently reported cardiac sympathetic dysfunction in the left ventricular wall in patients with Parkinson’s disease (PD). Whether the nerve fibers of the cardiac conduction system or the atrial walls are equally affected in this disease process has not yet been well documented. Therefore, the aim of this study was to investigate sympathetic nerves in the cardiac conduction system as well as in the walls of all four heart chambers in patients with PD, in incidental Lewy body disease (iLBD), and in controls. Heart tissue from five PD patients, two iLBD cases, and seven controls were investigated immunohistochemically using antibodies directed against tyrosine hydroxylase (TH) and α-synuclein (syn-1). A marked diminution of TH immunoreactivity (IR) within nerve fibers was observed in four PD patients and in both individuals with iLBD. In contrast, all control subjects displayed dense TH-IR nerve structures. The depletion in TH-IR involved not only the ventricles, but also the conduction system and the atrium showing a global change within cardiac TH-IR nerve fibers in the course of PD. In conclusion, the alterations in cardiac sympathetic nerves of patients with PD or in individuals with iLBD are homogeneous and global within the heart. The clinical implications related to this complete cardiac sympathetic dysfunction, including clinical correlates, diagnostic implications, and treatment, however, remain to be determined in a larger autopsy-controlled cohort of prospectively followed individuals.