We describe the case of a neonate who was prenatally diagnosed at a gestational age of 36 weeks with premature constriction of the ductus arteriosus. Blood from the thin ductus arteriosus flowed toward the pulmonary artery. Severe tricuspid regurgitation was also observed. We subsequently confirmed rupture of the tricuspid papillary muscle after birth. Cardiotonic drugs and nitric oxide were administered immediately at birth for pulmonary hypertension, and this therapy was continued until the seventh postnatal day. Emergency tricuspid valve repair was unnecessary, because there were no signs of severe circulatory insufficiency. This case suggests a relationship between prenatally diagnosed premature constriction of the ductus arteriosus and tricuspid papillary muscle rupture in neonates.