Conduction velocity is maximum in

Purkinje fibers lead from the A-V node through the A-V bundle into the ventricles. Except for the initial poion of these fibers where they penetrate the A-V fibrous barrier, they have functional characteristics that are quite the opposite of those of the A-V nodal fibers. They are very large fibers, even larger than the normal ventricular muscle fibers, and they transmit action potentials at a velocity of 1.5 to 4.0 m/sec, a velocity about six times that in the usual ventricular muscle and 150 times that in some of the A-V nodal fibers. The rapid transmission of action potentials is caused by very high level of permeability of the gap junctions at the intercalated discs between the successive cells that make up the prkinje fibres. They have very few myofibrils--contract little or not at all during the impulse transmission. Ref: Guyton and Hall textbook of medical physiology 13th edition. Page: 125