Objective   To investigate the protein and mRNA expression of hypoxia inducible factor-1α (HIF-1α) in the myocardium of infants with cyanotic congenital heart defects and the related significance.     Methods   A total of 28 children with cyanotic (n=16) or acyanotic cardiac defects (n=12) were investigated. Samples from the right ventricular myocardium taken immediately after aortic clamping were studied for protein and mRNA expression.     Results   Immunohistochemistry revealed HIF-1α expression both in the cytoplasm and nucleus. Protein level of HIF-1α increased significantly (P0.001) in patients with cyanotic as compared with that in patients with acyanotic congenital heart disease and inversely correlated with the degree of hypoxemia. No difference was found in HIF-1α mRNA expression between the two groups (P0.05).     Conclusion   Chronic hypoxemia may be associated with the induction and stabilization of the transcription factor HIF-1α. Thus

stabilization of HIF-1α and induction of the adaptive hypoxia response could particularly participate in myocardial adaptive metabolic effects in children with congenital cardiac defects and chronic hypoxemia.