Tracts of fibers that carry impulses from the AV node down throughout the ventricles. Starting in a bundle of electrical tracts called the Bundle of His and the tracts then branch into the right and left bundle branch. The right bundle branch carries impulses to the right ventricle; the left bundle branch carries impulses to the left ventricle. The left bundle further divides into two sub-branches called the anterior fascicle and posterior fascicle which each help to distribute or spread the impulse throughout the larger left ventricle.

The portion of the conduction system that from the bundle of His to the Purkinje fibers. The Bundle of His splits into a right bundle for the right ventricle and two left bundles for the left ventricle.