The cardiac neural elements which survive surgical denervation of the heart have been called the “intrinsic” innervation (ICN). These include postganglionic parasympathetic neurons and chromaffin cells. Specific activation of the ICN with nicotine (NIC) has been shown to produce powerful negative inotropic and chronotropic effects on the heart. The present study was performed to assess the influence of the ICN on dromotropic activity. Seven mongrel dogs successfully underwent surgical denervation of the heart. They were placed on cardiopulmonary bypass and conduction through the atrioventricular (AV) node as well as the right atrium was measured by an acrylic electrode plaque. Conduction through the right bundle branch (RBB) was measured using a second recording electrode. Drugs administered were acetylcholine (ACh, 0.1-10.0 μg); NIC (1-100 μg); and tetrodotoxin (TTX, 30 μg). All agents were injected by the intracoronary route. Both ACh and NIC caused significant increases in AV nodal conduction time; i.e., 5-49% and 11-49%, respectively. Intra-atrial, bundle branch, and His-to-ventricular muscle conduction was affected inconsistently, and the changes were nonsignificant. Responses to NIC, but not to ACh, were completely blocked by 30 μg of TTX. The effects of the ICN on ventricular conduction appear to parallel those of the parasympathetic innervation, i.e., profound influence on AV nodal conduction with little or no effect below this structure. In contrast, however, the ICN does not appear to affect intra-atrial conduction, nor do there appear to be functionally important chromaffin cells that affect conduction time.Circ Res 47: 74-79, 1980.