BACKGROUND Ventricular tachyarrhythmia is the leading cause of sudden cardiac death, and scroll wave re-entry is known to underlie this condition. Class III antiarrhythmic drugs are commonly used worldwide to treat ventricular tachyarrhythmias; however, these drugs have a proarrhythmic adverse effect and can cause Torsade de Pointes or ventricular fibrillation. Transmural dispersion of repolarization (TDR) has been suggested to be a strong indicator of ventricular tachyarrhythmia induction. However, the role of TDR during sustained scroll wave re-entry is poorly understood. The purpose of the present study was to investigate how TDR affects scroll wave behavior and to provide a novel analysis of the mechanisms that sustain tachyarrhythmias, using computer simulations. METHODS AND RESULTS Computer simulations were carried out to quantify the TDR and QT interval under a variety of I(Ks) and I(Kr) during transmural conduction. Simulated scroll wave re-entries were done under a variety of I(Ks) and I(Kr) in a ventricular wall slab model, and the scroll wave behavior and the filament dynamics (3-dimensional organizing center) were analyzed. A slight increase in TDR, but not in the QT interval, reflected antiarrhythmic properties resulting from the restraint of scroll wave breakup, whereas a marked increase in TDR was proarrhythmic, as a result of scroll wave breakup. CONCLUSIONS The TDR determines the sustainment of ventricular tachyarrhythmias, through control of the scroll wave filament dynamics.