A 67-year-old man who had cardiopulmonary arrest (CPA) at home was admitted to our institution. His spontaneous circulation was restored by bystander cardiopulmonary resuscitation (CPR) performed by his wife and an automated external defibrillator (AED). J waves were observed in the inferior leads of an electrocardiogram. We performed an implantable cardioverter defibrillator (ICD) implantation. After the ICD implantation, appropriate shocks due to ventricular fibrillation (VF) were observed on interrogation of the ICD at a frequency of twice a month. Most VF events occurred in the early morning between 1:00 to 6:00, and ventricular premature contractions (VPCs) were detected just before the occurrence of VF. Since the VF events always occurred in the early morning, we started long-acting disopyramide (150 mg/day, before bedtime), which has a muscarinic receptor blocking action. As a result, he has not received any appropriate ICD shocks for more than two years.