The mechanisms responsible for postshock behavior of the heart are poorly understood. Below threshold shocks may induce arrhythmias that are difficult to contain. Cardiac vulnerability to shocks and defibrillation efficacy are largely determined by the postshock activity during the occurrence of a brief electrically quiescent period, known as the isoelectric window (IW) and activations following the IW period. This paper presents a detailed computer simulation study that underlines the role of the Purkinje system (PS) in postshock arrhythmogenesis. Reentry was induced in an anatomically realistic rabbit heart model using three different shocking protocols. Regions of vulnerability were determined for each protocol with and without PS. The role of PS during reentry was studied by isolating the PS from myocardium at various instances. The earliest post-shock activations were observed originating from the PS which initiated the reentry. The PS was shown to facilitate the reentry induction at weaker shocks. The PS also helped to stabilize the reentry in the early stages but did not play any significant role in the later stages. This research provides valuable insights into the postshock arrhythmogenesis and maintenance, and extends the discussion on the occurrence of IW as observed during clinical and experimental studies.