Introduction: The significance of high precordial electrocardiograms in idiopathic ventricular fibrillation (IVF) is unknown. Method: This study included 50 consecutive patients (48 men; age, 42±18 years) who had spontaneous ventricular fibrillation not linked to structural heart disease and received implantable cardiac defibrillator therapy. IVF was diagnosed in 35 patients and Brugada syndrome was diagnosed in other 15 patients. Electrocardiograms in high intercostal space were compared between 35 patients with IVF and 105 age- and sex-matched healthy controls (patient: control ratio, 1:3). Results: The frequency of J point elevation ≥ 0.1mV in the 4th intercostal spaces was similar between patients with IVF (14%) and healthy controls (7%). However, the frequency of J point elevation ≥ 0.1mV in the 3rd intercostal space was higher in patients with IVF (40%) than controls (11%) (P < 0.01). J point elevation was present only in the 3rd intercostal space but not in the 4th intercostal space in 30% of patients with IVF but only in 6% of controls (P < 0.01). During follow up, the recurrence of ventricular fibrillation was higher in patients with IVF who had J point elevation in the 3rd intercostal space (36%) and Brugada syndrome(40%) than those with IVF who did not have J point elevation in the 3rd intercostal space.(11%) (P < 0.05 for both). Conclusion: J point elevation in the 3rd intercostal space was associated with IVF and recurrences of ventricular fibrillation. Electrocardiogram recordings in the high intercostal space may be useful to identify risk of sudden death.