Aim To study the protective effect of imidapril on cardiac function and mitochondrion of rats with diastolic heart failure. Methods 30 SD rats were randomly divided into 5 groups:control group, DHF group,A1.5mg,A3mg,and A6mg group.DHF model was produced by abdominal aortic coarctation in the rats in the operating group.The rats in A1.5mg-A6mg groups were given with imidapril [1.5,3,and 6 mg/(kg·d)] by intragastric administration for 4 weeks,the others were treated with equal isotonic NaCl.After 4 weeks,cardiac function and hemorheology was assessed by echocardiography and catheterization.Specimens were taken and ventricular mass were measured.The level of malonaldehyole(MDA),superoxidedismutase(SOD),and glutathioneperoxidase(GSHPx) were detected by spectrophotometer.Ultra structure changes in myocardium were observed under electrion microscopy. Results In DHF group,PW,IVS,LVM,E/A ratio,SBP,DBP,LVSP,LVEDP,and MDA were increased,Tau was prolonged,LV-dp/dtmax,SOD and GSHPx was decreased.The myocardium damage including abnormality of myofilament arrangement,mitochondrial swelling and vacuolization were showed.Compared with DHF group,increased E/A ratio,IVS,PW,LVM,SBP,DBP,LVSP,LVEDP and MDA were decreased,prolonged Tau was shorted,decreased LV-dp/dtmax,SOD and GSH-Px were increased in treated groups.The myocardium damage was ameliorated in treated groups too.The protective effect of Imidapril on heart was increased according to the increasing dose of it. Conclusion Imidapril improve cardiac function in rats with DHF by ameliorating the damage of myocardic cell and mitochondrion.