A case of fibromuscular dysplasia of the coronary arteries in a 15-year-old boy is reported. After a quarrel involving no violence the boy suddenly suffered from ventricular fibrillation, collapsed and was initially successfully defibrillated. After 37 days of deep unconsciousness the boy died of bronchopneumonia. The cause of the ventricular fibrillation was clarified only after histological investigations. Fibromuscular dysplasia of the coronary arteries with narrowing was found, which has very occasionally been described in the literature. However, its localization in the A-V node artery, as described here, only seems to have been observed once.