This velocity translates to 6 times that in normal cardiac muscle. This high rate of transmission of action potentials could be caused by a high level of permeability of the gap junctions at the intercalated discs between the successive cardiac cells that make up these purkinje fibers. Once the impulse reaches the purkinje fibers, it is transmitted through the ventricular muscle mass by the ventricular muscle fibers themselves. The velocity of transmission is now only around 0.3 tp 0.5 milliseconds, equating to one sixth that in the purkinje sysem. The cardiac muscle wraps around the heart in a double spiral.
Fibrous septa exist between the spiraling layers.
The cardiac impulse, therefore, does not travel directly outward toward the surface of the heart but instead angulates toward the surface along the directions of the spirals. For effective pumping of the ventricles to exist the purkinje sysem must send the action potential to almost all portions of the ventricles within in a short amount of time. This will allow both ventricles to begin contracting at around the same time.