|A 35-year-old male patient with heart and renal failure and pneumonia was transferred to our department due to recurrent cardiac standstill with seizure-like activity. He had been diagnosed as and treated for MELAS syndrome since 3 years ago. His electrocardiography (ECG) showed Wolff-Parkinson-White (WPW) pattern, and an echocardiogram showed hypertrophic cardiomyopathy (HCM). He developed seizure-like activities intermittently and ECG monitoring showed intermittent bradycardia. His Holter monitoring showed several episodes of 5 to 16 seconds of sinus arrest. We performed electrophysiologic study for evaluation of his arrhythmia. During atrial and ventricular extrastimuli, cardiac standstill has developed several times and the duration of pauses varied from 2.5 to 3.2 seconds. Abrupt asystolic events have also developed accompanying seizure-like activities which were not related to extrastimuli. We decided to implant a permanent pacemaker. After the implantation of DDD type pacemaker, the patient`s seizure-like activity disappeared.