Although a plethora of earlier studies focused on the histology and action potential characteristics of Purkinje fibers, only recently has the His-Purkinje system been found to play a major role in the genesis of cardiac arrhythmias. The anatomic complexity of the left ventricular conduction system appears to favor reentrant arrhythmias in both diseased and healthy hearts. Macroreentrant circuits between the right and left bundles as well as between the left ventricular fascicles are amenable to cure by ablative techniques. Similarly, fascicular tachycardias occurring in individuals without structural cardiac disease appear to involve macroreentrant circuits between fascicles and associated strands (false tendons?). Exciting newer discoveries strongly implicate the Purkinje system as the cause of ventricular arrhythmias in patients with short-coupled premature ventricular complexes and in those with catecholaminergic polymorphous ventricular tachycardia. The role of the His-Purkinje system in the genesis and maintenance of ventricular fibrillation is yet another frontier for fertile investigation. A rich variety of cardiac arrhythmias appears to involve the ventricular specialized conduction system and may be amenable to ablative therapy.