We report a patient with prenatally diagnosed tuberous sclerosis. Fetal ultrasonography demonstrated multiple cardiac tumors and arrhythmia. After birth, because of frequent supraventricular extrasystoles, the infant was admitted to the neonatal intensive care unit. Findings on 24-hour ambulatory electrocardiogram (ECG) showed frequent supraventricular tachycardia and ventricular tachycardia with four beats as the longest run. At the age of 12 days, he developed cardiopulmonary arrest after crying out. A monitored ECG showed ventricular tachycardia. Twenty minutes after onset, a 12-lead ECG showed ventricular fibrillation, which returned to normal sinus rhythm with repeated DC cardioversion. Oral antiarrhythmic therapy with carteolol hydrochloride was effective. The patient showed no further symptoms after oral medication was initiated and the tumors regressed spontaneously.