A 72-year-old male patient with idiopathic dilated cardiomyopathy who had shown recurrent episodes of drug refractory ventricular fibrillation underwent implantation of a transvenous implantable cardioverter defibrillator (ICD). Ventricular fibrillation (VF) was induced by a T wave shock at the implantation. However, the ICD device with a maximum energy of 30 J failed to terminate the VF. Reversing defibrillation polarity and/or adding a defibrillation electrode lead at the site of a high superior vena cava were also ineffective. The ICD was programmed to a maximum energy of 30 J when the device sensed spontaneous VF. During the follow-up period of 5 months, two episodes of spontaneous VF were recorded from ICD telemetry, and the ICD device terminated VF successfully with the first therapy shock in both episodes. No previous reports have shown failure to terminate induced VF at implantation of the ICD with successful termination of spontaneous VF during follow-up. Careful follow-up is needed in ICD patients, especially those with very high defibrillation thresholds.