Background: Congenital heart defects (CHDs) is the most common abnormality induced by pregestational diabetes mellitus (PGDM), but the exactly mechanism remains obscure.GATA4 plays a critical role in cardiogenesis and the regulation of cardiomyocyte proliferation and apoptosis.The expression level change of GATA4 lead to various of CHDs.We aimed to determine whether GATA4 is responsible for the teratogenesis induced by PGDM.Methods: In vivo, we analysed the morphological changes and the expression pattern of GATA4 at E13.5, E15.5, E18.5 developing embryo hearts of streptozotocin-induced PGDM mice and controls.The cardiomyocyte proliferation and apoptosis were assessed by the expression of PCNA and TUNEL assay in developing cardiac tissue.In vitro, we investigated the expression pattern of GATA4 on H9c2 cell in presence of high glucose.The proliferation and apoptosis of H9c2 cell were analysed by cell viability analysis and flow cytometry.Results: Morphological analysis displayed increased incidence of cardiac and extra-cardiac malformations in embryos of PGDM mice.GATA4 protein expression level dramatically reduced in the developing hearts of embryos from PGDM mice.The proliferation of cardiacmyocytes was supressed, whereas the apoptosis was increased in the embryonic hearts of PGDM mice.In vitro study exhibited reduction in GATA4 protein expression and decreased cell proliferation in H9c2 cells exposed to high glucose.Furthermore, high glucose induced H9c2 cell apoptosis remarkably.Conclusions: Our data demonstrate that the down-regulation of GATA4 expression which is of critical importance for the morphogenesis of heart could contribute to the congenital heart defects induced by pregestational diabetes mellitus.