
Figure 1: AV node as depicted by Sunao Tawara
The atrioventricular (AV) node is a critical component of the conduction system of the heart, serving as the only (normal) electrical connection between the atria and the ventricles. By delaying atrioventricular transmission by 1/10th of a second, the AV node allows the heart to work as a pump.
The AV node is situated in the inferior portion of the interatrial septum. It was discovered in 1906 by Sunao Tawara, who identified it as a discrete small structure located at the atrioventricular junction and demonstrated continuity of the AV node with the His–Purkinje system (see image 1).
The AV node is a located in the “Triangle of Koch” (see note), a region bound by the tendon of Todaro, the septal leaflet of the tricuspid valve, and the ostium of the coronary sinus (see image 2). Its blood supply is by way of the AV node artery, a branch of the right coronary artery (RCA) that arises usually at the crux cordis, the point of division of the RCA into the posterior descending artery and posterolateral artery.
Image 2: SVC: Superior vena cava, RPA: Right pulmonary artery, RSPV: Right superior pulmonary vein, RIPV: Right inferior pulmonary vein, IVC: Inferior vena cava, RAA: Right atrial appendage, FO: Foramen ovale, TV: Septal leaflet of the tricuspid valve. The yellow line shows the location of the "Tendon of Todaro". The complete triangle is the triangle of Koch.
The ventricles are isolated from the atria by connective tissue that forms an electrical barrier between. This barrier is sometimes called the “skeleton of the heart” a misnomer that does not explain the reason for its presence. If there was no barrier, the atria and ventricles would all contract at the same time and the pumping action of the heart would not exist.
The only place where the electrical impulse can pass from the atria to the ventricles is through the AV node. Because of the specialized cardiomyocytes that form the node, the transmission of the impulse is delayed by one tenth of a second, enough that the ventricles will contract after the atria contract, causing blood flow through the heart.
Note: The "triangle of Koch" is eponymically named after Walter Eduard Carl Koch (1880 - 1962) a German physician and pathologist.
Sources and References:
1. Markowitz, MM; Lerman BL. A contemporary view of atrioventricular nodal physiology. J Interv Card Electrophysiol. 2018 Aug;52(3):271-279.
2. Efimov IR, Nikolski VP, Rothenberg F, Greener ID, Li J, Dobrzynski H, Boyett M. Structure-function relationship in the AV junction. Anat Rec A Discov Mol Cell Evol Biol. 2004 Oct;280(2):952-65.
3.Fumarulo I, Salerno ENM, De Prisco A, Ravenna SE, Grimaldi MC, Burzotta F, Aspromonte N. Atrioventricular Node Dysfunction in Heart Failure: New Horizons from Pathophysiology to Therapeutic Perspectives. J Cardiovasc Dev Dis. 2025 Aug 15;12(8):310.
4. Anderson RH, Sánchez-Quintana D, Nevado-Medina J, Spicer DE, Tretter JT, Lamers WH, Hu Z, Cook AC, Sternick EB, Katritsis DG. The Anatomy of the Atrioventricular Node. J of Cardiovasc Development and Disease. 2025; 12(7):245.
5. Tawara, S. Das Reizleitungenssystem des Säugetierherzens : eine anatomisch-histologische Studie über das Atrioventrikularbündel und die Purkinjeschen Fäden 1906 J Fischer pub. courtesy of archive.org
6. "Tratado de Anatomia Humana" Testut et Latarjet 8th Ed. 1931 Salvat Editores, Spain
7. Anderson, Robert H. MD; Becker, Anton E. MD. "Slide Atlas of Cardiac Anatomy" 10 volumes London: Gower Medical Publishing, 1985. (out of print)



