Boundary of the Koch's triangle is not formed by

The atrioventricular node (AVN) is within the subendocardial layer of the hea wall of the interatrial septum. In relation to the right atrium, its position is within the triangle of Koch Triangle of Koch: a roughly triangular area on the septal wall of the right atrium, bounded by the base of the septal leaflet of the tricuspid valve, the anteromedial margin of the orifice of the coronary sinus, and the tendon of Todaro; it marks the site of the atrioventricular node. Tendon of Todaro: A palpable subendocardial collagen bundle in the wall of the right atrium, extending from the central fibrous body (fibrous skeleton of hea) across the torus aoicus toward the medial extremity of the valve of the inferior vena cava. Ref - pubmed.com