Abstract These studies were designed to examine the electrophysiological effects of lidocaine on distal Purkinje fibers of the canine heart. Standard microelectrode techniques were used to record transmembrane action potentials from the right bundle branch, free running strands of Purkinje tissue, and ventricular muscle. The duration of action potentials was maximal in the distal Purkinje fibers. The long duration of action potentials in these distal fibers determined the functional refractory period of the Purkinje-muscle junction. Early premature beats initiated on either side of the distal Purkinje fibers propagated with decrement or were blocked. Lidocaine shortened the action potential of Purkinje fibers but had little effect on muscle. The effect of lidocaine on action potential duration was dose dependent and was maximal in these distal Purkinje fibers. As a consequence of its ability to shorten action potential duration, lidocaine reduced the degree of nonuniformity of recovery of excitability. Lidocaine shortened the functional refractory period of distal Purkinje fibers and abolished decremental conduction of early premature beats. These effects may contribute to the antiarrhythmic actions of lidocaine.