Right atrium and tricuspid valve. The atrioventricular node (1) is the middle of the scene. The his bundle between the muscular (2) and the membranous septum continues with the right bundle branch (3). The blood supply of the atrioventricular node is double in this case. The inferior septal nodal artery (A). branch from inferior and right superior septal artery (D) arising from the origin of the right coronary artery.