Schematic representation of the atrioventricular bunle of His. The bundle, represented in red, originates near the orifice of the coronary sinus, undergoes slight enlargement to form the AV node. The AV node tapers down into the bundle of HIS, which passes into the ventricular septum and divides into two bundle branches, the left and right bundles. Sometimes the 'left and right bundles of His' are called Purkyne or Purkinge fibres. The ultimate distribution cannot be completely shown in this diagram.