A unique and complex pattern of intraventricular trifascicular block was documented electrocardiographically, for the first time, in a newborn infant with a history of transient intrauterine bradycardia. The clinical course was progressive, leading to a high-degree atrioventricular block, accompanied by severe Adams-Stokes attacks and congestive heart failure. Pacemaker therapy had to be instituted at the age of 3 months. Congenital intraventricular trifascicular block differs from the usual form of congenital heart block. It deserves close observation and early therapeutic intervention.