A 21-year-old woman, without medical history, was admitted after cardiac arrest. Cardiopulmonary resuscitation and use of semiautomatic defibrillator quickly restored sinus rhythm. Clinical examination was normal with no cardiac murmur or abnormal heart sound. Electrocardiogram revealed sinus rhythm with short QT interval. Serum electrolytes and arterial blood gazes were normal. One hour after admission, lethal ventricular fibrillation occurred. Factors that shorten QT interval including increase in heart rate, hyperthermia, increased calcium, or potassium plasma levels and acidosis were excluded. Short-QT syndrome has been recently recognized as a genetic ion channel dysfunction leading to an abbreviation of action potential and a potential substrate for arrhythmias. This syndrome is characterized by a short QT interval (typically <320 milliseconds), associated with a high incidence of sudden death, syncope, or atrial fibrillation in individuals with an apparently normal heart. Implementation of an internal cardiac defibrillator remains the only effective preventive treatment.