A 58-year-old male patient had apical hypertrophic cardiomyopathy (HCM) associated with a life-threatening tachycardia due to atrial flutter. Following palpitation and dyspnea for 2-3 h, he became unconscious because of circulatory catastrophe, but was fully resuscitated. An electrocardiogram recorded just before the loss of consciousness revealed atrial flutter at a rate of 260 beats/min with a 2:1 ventricular response. He was diagnosed as having apical HCM based on the echocardiographic and left ventriculographic findings. Atrial stimulation at a rate of 150 pacings/min for 1 min caused a marked drop in systemic systolic blood pressure from 170 to 120 mmHg. The patient was treated with 150 mg of cibenzoline per day to prevent supraventricular tachyarrhythmias and to improve left ventricular diastolic function. At the time of the recent follow-up at 2 and a half years, he felt quite well.