Atrioventricular node

The atrioventricular (AV) node is a specialized cardiac structure that serves as the sole electrical connection between the atria and ventricles in the normal heart. It is responsible for delaying electrical impulses to allow proper ventricular filling before contraction and filtering rapid atrial impulses to protect the ventricles from life-threatening arrhythmias.

In dogs, the AV node is approximately 1.5 mm in diameter, and shows little histologic differentiation from the bundle. It begins in the septal wall of the atrium approximately 5 mm cranioventral to the opening of the coronary sinus and craniodorsal to the septal cusp of the right atrioventricular valve. From this apparently blind beginning, the atrioventricular bundle runs cranial and ventral through the fibrous base of the heart and then divides into right and left branches.