In premature, very-low-birth-weight (VLBW) neonates, complex cardiac malformations can be successfully repaired under conditions of cardiopulmonary bypass. However, due to the immaturity of organ systems, these patients are exposed to a specific risk resulting from noxious effects of extracorporeal circulation, especially on the central nervous system. Two premature neonates with low and very low birth weight of 1160 g and 1650 g, were operated on using cardiopulmonary bypass for severe pulmonary artery stenosis and truncus arteriosus communis type II, respectively. The neonate with pulmonary valve stenosis survived, but at 2-year-follow-up examination motoricity retardation as a result of cerebral immaturity-related changes was evident. The other neonate died suddenly on the fifth postoperative day of a massive intracranial haemorrhage. Due to the fact that the natural history of VLBW children is a priori characterized by a high incidence of major neurological handicaps, open heart surgery may by improving survival chances contribute to an increased incidence of mentally handicapped children.