A 34-year-old woman was brought to our emergency department because of sudden loss of consciousness. Ventricular tachycardia and fibrillation were noted on electrocardiographic monitoring and reverted to sinus rhythm after repeated defibrillation. She was treated as a case of thyroid storm. Although tachycardia and fever normalized after 2 days, she remained comatose and died. This is an unusual case because the patient’s initial presentation was cardiac arrest without previous history of cardiac disease. To our knowledge, this is the first reported case where ventricular tachyarrhythmia was the initial presenting sign of thyroid storm.