After injection of 6-[18F]fluorodopamine, thoracic positron emission tomographic scanning visualizes the sympathetic innervation of the heart. This report introduces a kinetic model that relates 6-[18F]fluorodopamine positron emission tomographic scanning results to specific aspects of cardiac sympathoneural function. Inputs were the 6-[18F]fluorodopamine concentration in arterial blood and the estimated contribution of circulating metabolites of 6-[18F]fluorodopamine. All of the three compartments in the model were intraneuronal. Two compartments corresponded to vesicles in sympathetic nerves, consistent with the "multiple vesicular pool" hypothesis from preclinical studies. The model successfully fit the empirical time-activity curve for myocardial 6-[18F]fluorodopamine-derived radioactivity and predicted correctly the effects of several neuropharmacological and physiological manipulations on the time-activity curve. Myocardial cell uptake of metabolites of 6-[18F]fluorodopamine from the circulation could explain an immediate peak of 6-[18F]fluorodopamine-derived radioactivity. The model seems useful in predicting effects of altered cardiac sympathetic function on time-activity curves for myocardial 6-[18F]fluorodopamine-derived radioactivity in humans.