BACKGROUND: A substantial number of patients with idiopathic ventricular fibrillation (IVF) present with no specific electrocardiographic (ECG) findings. OBJECTIVE: To evaluate complete right bundle branch block (RBBB) among IVF patients. METHODS: IVF patients showing complete RBBB were included in the present study. Structural and primary electrical diseases were excluded, and provocation tests were performed to exclude the presence of spastic angina or Brugada syndrome (BrS). The prevalence of complete RBBB and the clinical and ECG parameters were compared either with IVF patients without RBBB or with the general population and age and sex comparable control with RBBB. RESULTS: Out of 96 IVF patients, 9 patients were excluded for the presence of BrS. Out of 87 patients studied, 10 (11.5%) patients revealed complete RBBB. None had structural heart diseases, BrS or coronary spasms. Average age was 44±15 years, and 8 of the 10 were male. Among the ECG parameters, only the QRS duration was different from the other IVF patients without complete RBBB. VF recurred in three: two in the form of storms which were well suppressed by isoproterenol. Complete RBBB was found less often in control subjects (1.37%, P<0.0001), and the QRS duration was more prolonged in the IVF patients:139±10 versus 150±14 ms (P=0.0061). CONCLUSION: Complete RBBB exists more often among IVF patients than in controls. A prolonged QRS complex suggests a conduction abnormality. Our findings warrant further investigation of the role of RBBB in the development of arrhythmias among patients with IVF. (243 words).