Aim To determine the effects of irbesartan on gap junction remodeling and expression of connexin 43(Cx43) in left cardiac ventricle of congestive heart failure(CHF) rats. Methods A heart failure model of experimental pressure overload induced by surgical abdominal aortic stenosis in adult SD rats was used.The rats with heart failure were confirmed by measuring the hemodynamic parameters and divided randomly into the group treated with irbesartan(50 mg/kg) and placebo.Sham-operated(PS) group rats served as negative controls after 16 weeks.Sixteen weeks later,gap junction remodeling in left cardiac ventricle of rats in sham-operated group,the irbesartan group,and placebo group was characterized by immunoblotting and electron microscopy. Results Compared with Sham-operated group,the expression of Cx43 in left ventricles from failing hearts in the placebo group was decreased 25.7%(0.929±0.095 vs 1.250±0.083,p<0.05),the expression of Cx43 in left ventricles from irbesartan group increased to the same level of Sham-operated group.Electron microscopy of LV tissue revealed that in contrast to left ventricles myocytes from Sham-operated group,which showed Cx43 labeling largely confined to the intercalated disks,left ventricles myocytes from rats in placebo group showed dispersion of punctate Cx43 labeling over the entire cell surface.The proportion of Cx43 label at the intercalated disk decreased significantly.In rats from irbesartan group,the gap junction disorganization was markedly reduced. Conclusion In left ventricles from failing hearts,the expression of Cx43 decreased,while the expression of Cx43 in left ventricles from rats treated with irbesartan increased significantly.Meanwhile,Irbesartan can improve space-remodling of gap junction in failing hearts.