It sits within an anatomic region bordered posteriorly by the coronary sinus ostium, superiorly by the tendon of Todaro, and anteriorly by the septal tricuspid valve annulus. The atrioventricular node (AV) is a subendocardial structure situated in the inferior-posterior right atrium. The sinoatrial node (SA) is the default pacemaker and is located subepicardially and is crescent in shape.
