We defined the central circuit innervating various regions of the rat heart using a neurotropic herpesvirus as a transneuronal tracer. Location of viral antigens in the brain after cardiac injection of three strains of pseudorabies virus (PRV) provided insight into vagal preganglionic neurons and their connected interneurons. At short survival times, labeled vagal preganglionic neurons were localized in both the nucleus ambiguus (NA) and the dorsal motor nucleus of the vagus (DMV), and in an arc-like band through the reticular formation between the NA and the DMV. The amount of DMV labeling was dependent on viral strain. Similar distributions of labeled neurons were observed following either ganglionic, sinoatrial node, or ventricular injections. At intermediate survival times postcardiac injection, the virus replicated in vagal preganglionic neurons and was trans- synaptically transported to interneurons observed primarily in the NA regions and in an arc-like band through the reticular formation. Labeled neurons were also observed in ventral regions of the nucleus of the solitary tract (NTS). At longer survival times, labeled neurons were found in various regions of the NTS with the most abundant label dorsal and dorsomedial to the solitary tract. Abundant neuronal labeling was also found in the intermediolateral cell column, the raphe nuclei, the caudal and rostral ventral lateral medulla, the A5 region, the locus coeruleus, and the lateral and paraventricular hypothalamic nuclei. These data define the central circuits including the interneuronal connections that innervate various cardiac targets.