During repair of a congenital heart defect the child is exposed to myocardial hypoxia. Recent studies have suggested that the paediatric myocardium is more sensitive to hypoxia and cardioplegic arrest than the adult. The protective effect of halogenated agents on ischaemia and reperfusion injury has been investigated widely in adults. The investigators hypothesis that sevoflurane applied during cardiopulmonary bypass might afford better myocardial protection during paediatric cardiac surgery.