A 15-year-old girl, who was previously in good health, suddenly collapsed while jogging. Immediate cardiopulmonary resuscitation (CPR) was initiated, and she arrived at our hospital 13 minutes later. The ventricular fibrillation (VF) on admission was reverted to sinus rhythm 18 minutes after collapse by the second cardioversion. The echocardiogram revealed hypertrophic nonobstructed cardiomyopathy (HNOCM), although the 24hr ambulatory electrocardiographic, electrophysiologic and exercise stress tests could not define the exact cause of VF. Exercise-induced ischemia with sustained mild hypokalemia was suspected to be the cause of VF. The patient recovered consciousness three days after admission, and followed an uneventful course of treatment with oral atenolol not associating with disabling neurological deficit. Immediate basic life support and delivery of automatic external defibrillator on the spot is needed to rescue patients with out-of-hospital cardiac arrest