Conduction continues to the Bundle of His.
This Bundle of His passes into the interventricular septum before dividing into left and right branches to form the complex network of Purkinje fibers that depolarizes both ventricles.
The Purkinje fibers penetrate the inner one-third of the endocardium, and the electrical impulse spreads through myocardial muscle to the epicardium, providing for simultaneous depolarization of both ventricles.
The right bundle travels intramyocardially to the apex and the anterior papillary muscle of the right ventricle.
The left bundle branch can have variable anatomy, but is traditionally thought of having an anterior and a posterior fascicle, coursing to the anterolateral and posteromedial papillary muscles of the left ventricle. The main left bundle bifurcates into two primary subdivisions: a left anterior fascicle and a left posterior fascicle. The depolarization wavefronts then spread through the ventricular wall, from endocardium to epicardium.
In normal cardiac electrophysiology, the electrical conduction occurs from left to right, essentially stimulating the left bundle and left ventricle first.
The blood supply to the upper muscular interventricular septum is via the left anterior descending and posterior descending arteries.
This dual vascular supply can protect the conduction system at this level from ischemic events.