A woman in her 50s was brought to the emergency department after she collapsed, received chest compressions from her husband, and recovered consciousness at home. On admission, the patient was conscious without any discomfort. Vital signs were normal and physical examination was unremarkable. A 12-lead electrocardiogram (ECG) on admission was recorded (Figure, A). Shortly after admission, continuous ECG monitoring (Figure, B) revealed recurrent episodes of polymorphic ventricular tachycardia (VT). Although most episodes did not sustain, some deteriorated into ventricular fibrillation (VF) associated with loss of consciousness and required direct current cardioversion. Intravenous infusions of lidocaine, amiodarone, magnesium, and isoproterenol failed to prevent recurrence of these malignant arrhythmias. Serum electrolyte levels were normal. Transthoracic echocardiography showed normal cardiac function and structure. Emergency coronary angiography showed no evidence of obstructive coronary artery disease. A temporary transvenous right ventricular pacemaker was inserted. However, ventricular overdrive pacing was not effective in suppressing the polymorphic VT. Her condition deteriorated and, over the next hour, she required direct current cardioversion 12 times.