The atrioventricular bundle is the extension of the atrioventricular node from the atrium across the fibrous skeleton of the heart to the ventricles. It passes from the anterior and inferior part of the AVN as a group of specialised myocytes within an insulating sheath of connective tissue. Then, the bundle of fibres runs slightly superiorly through a unique channel within the central fibrous body. At this point, it is deep to the line of attachment of the septal leaflet of the tricuspid valve.
Next, the bundle passes along the posterior and inferior margin of the pars membranacea septi to reach its junction with the superior margin of the muscular interventricular septum. At this point, the main AV bundle divides into two bundle branches to the respective ventricles.
Histologically, the common bundle is largely composed of transitional myocytes. These cells exhibit features intermediate to contractile myocytes and specialised Purkinje cells. The connective tissue surrounding the bundle prevents depolarisation of the ventricular myocardium in direct with it during its course through the interventricular septum.