<p>The exact location of the dominant pacemaker site in adult bird heart continues to be ill-defined. The aim of this study was to identify the localization of the dominant pacemaker and to investigate its electrophysiological characteristics in isolated sinoatrial preparations of the adult chicken <i>(Gallus gallus domesticus)</i> heart. The dominant pacemaker was localized at the base of the right leaflet of the valve of the right cranial vena cava and at the base of both leaflets of the valve of the caudal vena cava. But latent pacemakers were also identified in regions around these valves. Additionally, the valve leaflets generated conducting-like APs that with high amplitude, fast maximal upstroke velocity (greater than in working myocardium) and with diastolic depolarization. The avian sinoatrial junction is electrophysiologically heterogeneous. The avian dominant pacemaker site is more extensive than that in mammals. These findings establish a foundation for understanding species-specific pacemaker mechanisms and their evolution.</p>