The Purkinje network is one of the electrical excitation conduction systems in the heart and represents the most distal portion of the ventricular conduction system. Gap junction channels provide a pathway for electrical signaling between cells. A recent study identified a mutation that reduces the gap junction conductance in patients with ventricular arrhythmias. To elucidate underlying mechanisms, we studied the relationship between gap junction conductance in the Purkinje network and ventricular arrhythmias using computer simulations. We constructed His-Purkinje-ventricular network models composed of ≈13,000 cells, in which neighbouring cells were connected by gap junction channels. At lower gap junction conductances, reentrant beats occurred. When one of the reentrant circuits was disconnected, reentrant beats did not persist in many cases as a consequence of altering dynamics in excitation conduction. Our simulation results suggest that both Purkinje network structure and gap junction conductance are important factors for generating arrhythmias in the Purkinje network.