A female infant with isolated noncompaction of ventricular myocardium who developed ventricular tachyarrhythmia is described. Wolff-Parkinson-White syndrome was shown by electrocardiography. At 9 months of age, the patient suddenly developed cardiac arrest. Electrocardiography following resuscitation with DC cardioversion demonstrated sinus rhythm without delta wave. The QT interval was normal. Frequent premature ventricular captures caused ventricular fibrillation. DC cardioversion was necessary to terminate frequent attacks of ventricular fibrillation until the introduction of beta blockers and lidocaine. Two-dimensional echocardiogram confirmed the diagnosis of isolated non-compaction of ventricular myocardium. Three months later, the patient died of ventricular fibrillation during respiratory syncytial viral infection.