There is substantial interest in identifying biomarkers to detect early Parkinson disease (PD). Cardiac noradrenergic denervation and attenuated baroreflex-cardiovagal function occur in de novo PD, but whether these abnormalities can precede PD has been unknown. Here we report the case of a patient who had profoundly decreased left ventricular myocardial 6-[18F]fluorodopamine-derived radioactivity and low baroreflex-cardiovagal gain, 4 years before the onset of symptoms and signs of PD. The results lead us to hypothesize that cardiac noradrenergic denervation and decreased baroreflex-cardiovagal function may occur early in the pathogenesis of PD.