Abstract: Objective This study was designed to investigate effects of AT 1 receptor antagonist （losartan） and ACE inhibitor （fosinopril） on cardiomyocyte apoptosis,myocardial fibrosis,and angiotensin Ⅱ （Ang Ⅱ） in the left ventricle of spontaneously hypertensive rats （SHR）. Methods This study was performed in 30 SHRs of 16 week old. The rats were randomized to three groups:SHR L（losartan,30 mg·kg -1 ·d -1 ）,SHR F（fosinopril,10 mg·kg -1 ·d -1 ）,and SHR C （placebo）,each group consisting of 10 rats. 5 rats randomly obtained from each group were killed at 8 weeks and 16 weeks of the study respectively. The cardiomyocyte apoptosis was examined by in situ TDT mediated dUTP nick end labeling （TUNEL）. The parameters of myocardial fibrosis such as collagen volume fraction（CVF） and perivascular collagen area（PVCA） were determined by pathological examination with computed processing. Ang Ⅱ concentrations of plasma and myocardium were measured by radioimmunoassay. Results The results showed that: （1） Compared with SHR C at 8 weeks and 16 weeks systolic blood pressure was decreased similarly in the both treatment groups. Left ventricular weight and left ventricular mass indexes were lower significantly in the both treatment groups. The left ventricular mass index at 16 weeks was reduced to a lesser extent in SHR F group than that in SHR L group. （2）Compared with SHR C,the cardiomycyte apoptotic index（APOI） at 8 weeks was reduced significantly only in SHR F group,and at 16 weeks in both treatment groups. The APOI of SHR F group was lower than that of SHR L group at 16 weeks. （3）Compared with SHR C, CVF and PVCA at 8 weeks and 16 weeks were reduced significantly in the SHRs treated with either fosinopril or losartan. However,CVF at the latter endpoint in the SHR F was lower than in the SHR L. （4）Compared with SHR C,plasma and myocardium Ang Ⅱ levels at both endpoints were increased significantly in SHR L. However,plasma Ang Ⅱ levels were not changed,and myocardium Ang Ⅱ levels reduced significantly at 8 weeks and 16 weeks in SHR F group. Conclusion These results indicate that either of losartan and fosinopril effectively inhibits cardiomyocyte apoptosis and myocardial fibrosis, and reverses heart hypertrophy. Fosinopril may be more effective in these cardioprotective effects. The effects of ACEI or AT 1 antagonist on myocardiocyte apoptosis,myocardial fibrosis and left ventricular hypertrophy were related to inhibition of myocardium renin angiotensin system.