Background. Idiopathic ventricular fibrillation occurring in patients with background early repolarization and transient augmentation of J waves (IVF-ER-J) has been described. The present study evaluates the mode of VF initiation in patients with IVF-ER-J compared with those with typical Brugada syndrome (BrS). Methods. The mode of the onset and the coupling intervals of the PVCs initiating VF episodes were analyzed in patients with BrS (n=8) or IVF-ER-J (n=11) who experienced sudden cardiac death/syncope or repeat ICD shocks. Results. From a total of 50 patients with VF in the absence of structural heart diseases, 11 patients showed background ER in the resting ECGs. Among the 11 patients with IVF-ER-J, 5 presented with electrical storm (ES, more than 3 recurrent VF episodes/day). The 5 ES patients displayed a prominent but transient accentuation of J waves across the precordial and limb leads prior to development of ES. VF episodes were more commonly initiated by PVCs with a short-long-short (SLS) sequence in IVF-ER ES (42/58, 72.4%) than in BrS patients (13/86, 15.1%, p<0.01). Coupling intervals were significantly shorter in the IVF-ER-J patients as compared with those with BrS (307짹53ms vs. 409짹101ms, p<0.01). Pause following PVCs induced QT and Tpeak to Tend interval prolongation in the right precodial leads, suggesting a transient increase in dispersion of ventricular repolarization. Conclusion. Short-long-short sequence and PVCs with short coupling intervals were more frequently observed in patients with IVF-ER-J compared with those with BrS. This unique pause-dependent mode of initiation could potentially be applied in prevention of VF episodes in patients with IVF-ER-J.