Abstract: Objective To investigate dynamic changes of cardiomyocyte apoptosis and myocardial fibrosis during the development of cardiac hypertrophy in the spontaneously hypertensive rats（SHR）. Methods We studied the hearts specimens from 16,24 and 32 weeks old SHRs and age matched Wister Kyoto rats（WKY）. Cardiomyocyte apoptosis was identified by in situ TDT mediated dUTP nick end labeling（TUNEL）. The collagen volume fraction （CVF） and perivascular circumferential area （PVCA） were measured by pathological examination. The plasma and myocardium angiotensinⅡ were determined by radioimmunoassay. Results The results showed that（1）The systolic blood pressure,heart and left ventricular weights and left ventricular mass index were higher significantly in the SHRs of three age groups than in the WKY rats of age matched groups. （2） Compared with the WKY rats of age matched groups,the apoptotic index,CVF and PVCA were increased significantly, but no significant differences found among three groups in SHRs. （3）Plasma and myocardium angiotensinⅡ were increased significantly in the SHRs,and were positively correlated with cardiomyocyte apoptotic index and CVF respectively. Conclusion Myocardium angiotensinⅡ is one of potential mechamisms in induction of cardiomyocyte apoptosis and myocardial fibrosis.