Congenital heart defects are the most prevalent group of congenital malformations in newborns. Surgery-related low cardiac output syndrome (LCOS) could be one of the reason for the unfavourable outcome of this population. The early use of inodilators (INDs), specifically milrinone (MR), is proposed to reduce afterload and increase inotropism. Studies in the paediatric population appear to support a clinical usefulness of MR similar to that observed in adults. Levosimendan (LEVO) is a novel class IND developed for the treatment of heart failure. Experience with LEVO in paediatric patients is scarce. The purpose of this study was to systematically test the efficacy and safety of milrinone (MR) and levosimendan (LEVO) in newborns undergoing cardiovascular surgery with cardiopulmonary bypass (CPB). Given the uncertainty about LEVO pharmacokinetics in neonates, the study was designed as a pilot, phase I feasibility study.