Anatomy of the A–V node of the dog

Abstract The A‐V node of the dog is composed of closely interwoven fibers which frequently connect with each other within a sparse collagen framework. Fibers from the interatrial septum enter the posterior half of the node along its superior and posterior margins, while the anterior half of the node is isolated from such connections. In addition there are fibers from the interatrial septum which bypass these marginal atrionodal junctions and instead enter the convex surface of the node, which lies beneath the right atrial endocardium. These bypassing fibers circumvent most of the interweaving fibers within the A‐V node. At the posterior margin of the node, lying between it and the coronary sinus, there are ganglia and nerves, with the nerve fibers extending anteriorly through the A‐V node into the A‐V bundle. The only major anatomic difference between the human and canine A‐V nodes is their arterial blood supply, that of man being derived from one source originating from the right coronary artery and that of the dog being from two sources, both of which originate from the left coronary artery.