Background: It has been known that the shorter preceding diastolic interval (DI) is followed by shorter refractoriness and vulnerable to wavebreak resulting in maintenance of ventricular tachyarrhythmia (VT); restitution property. We hypothesized that initial diastolic interval determines whether VT sustains (SVT) or non-sustains (NSVT) during programmed ventricular stimulation (PVS) in human. Methods: We analyzed the monophasic action potential (MAP) recordings at the time of VT induction during PVS in clinically documented VT patients (n=12, 11 male, 50.8짹12.6 years old). 8 (66.7%; 4 Brugada syndrome, 2 right ventricular outflow tract VT, 1 left ventricular outflow tract VT, and 1 idiopathic ventricular fibrillation) of them had structurally normal heart, and 4 (33.3%; 1 post-myocardial infarction, 3 dilated cardiomyopathy) did not. PVS was performed by single to triple extra-stimuli with basic cycle length 600 ms, 400 ms, and 350 ms at right ventricular (RV) apex and RV outflow tract, respectively. We compared the initial preceding DI to the first beat of VT (DIn-1) and MAP duration at 90% repolarization (MAPD90) at the induction of SVT (n=26; sustained > 10 sec, requiring defibrillation or pace-termination) and NSVT (n=9). Results: 1) DIn-1 of SVT (87.2짹69.6 ms) was significantly shorter than those of NSVT (205.8짹53.6 ms, p=0.004). However, this difference became attenuated in patients with structural heart disease (205.85짹3.6 ms in NSVT vs. 103.3짹91.8 ms in SVT, p=0.073). 2) DIn-1 had positive correlation with following MAPD90 at the induction of SVT (r=0.6, p<0.05), but not at the induction of NSVT (p=NS). Conclusion: Significantly shorter DI after PVS was followed by shorter MAPD90 of 1st beat of induced ventricular rhythm, which resulted in sustaining self-perpetuation of VT. This finding suggests that repolarization restitution plays major role in the initiation and maintenance of VT in human.