Fatal paroxysmal supraventricular tachycardia in an infant.

A 37-day-old infant, without associated congenital anomalies, died following a 48-hour episode of supraventricular tachycardia. The histopathologic findings of nodoventricular and fasciculoventricular Mahaim's fibers in a setting of persistent fetal dispersion were consistent with an anatomic substrate for a reentry circuit at the specialized A-V junction.