Seven cases of heart arrest or pronounced bradycardia during 308 correct catheterizations of the umbilical vein in the first hours of life are reported. The indications for the catheterization were: 1. unsuccessful catheterization of the umbilical arteries in newborns with respiratory distress or post-asphyxia syndrome; 2. exchange transfusions for severe neonatal hyperbilirubinemia or sepsis; 3. monitoring the central vein pressure in severely compromised shocky newborns. Cardiac massage was always effective, at least temporarily, in restoring the heart activity. However, only three infants survived. Two of them had normal follow-up reported at 6 and 12 months respectively. The immediate risks and the necessary precautions for carrying out umbilical vein catheterization in severely ill newborns in the first hours of life are stressed.