Umbilical venous catheterization is frequently used for vascular access during neonatal resuscitation. The differentiation between umbilical artery and vein, specifically during the resuscitation procedure, is clinically neither always easy nor unambiguous. A preterm infant of 35 weeks of gestational age was born after an uneventful course of his mother's pregnancy. Severe postnatal cyanosis led to the placement of presumed arterial and venous umbilical catheters. Chest x-ray was suggestive of the presence of a persistent right umbilical vein (PRUV). Echocardiography showed a double outlet right ventricle with mitral atresia and a levo-atrial cardinal vein draining the left atrium into the azygos vein. The foramen ovale was firmly closed and conventional balloon atrioseptostomy failed. Several attempts of transseptal puncture and subsequent creation of an atrial septal defect were unsuccessful and the infant eventually died. There is an association of PRUV and congenital cardiac malformation. PRUV can be diagnosed prenatally if specifically looked for. The presence of PRUV can be the only clue prenatally alerting to the presence of congenital heart disease. Postnatal diagnosis of PRUV may justify echocardiography and cardiologic assessment even in the absence of clinical cyanosis.