AV node artery, and sampling of the AV node and bundle of His in the adult.   A. Right lateral view of parasagittal section of the heart showing the septal leaflet of the tricuspid valve, the lower margin of the atrial septum and the upper portion of the interventricular septum. The right coronary artery is seen in the atrioventricular sulcus on the left side of the image. B . A flap of atrial endocardium has been dissected to expose the AV nodal artery, shown here as it branches off the right coronary artery and penetrates the muscular portion of the interventricular septum. This artery is a useful landmark to identify the location of the AV node (arrwheads) and the bundle of His when the conduction system is sampled in coronal sections for microscopic examination . C to F . This sequence of panels shows the steps for sampling the AV node. The landmarks of the triangle of Koch are easier to identify in the adult. Several sections perpendicular to the line of insertion of the septal leaflet of the tricuspid valve are made as shown in D and are then processed for histologic study.