The impulse first enters the ventricular myocardium from the left bundle on the left side of the interventricular septum some distance beneath the aortic valve. It spreads across the interventricular septum from the left ventricular side to the right ventricular side. The right bundle branch is insulated from the ventricular myocardium until its termination in the anterior papillary muscle of the right ventricle. Its first functional contact with the right ventricle occurs here.