Aim To study the relation of myocardial apoptosis and interstitial fibrosis in non-infarct zone during the subsequent stages after infarction and its mechanisms by setting up an infarcted model of rat. Methods 10-12 femal rats underwent sham operation or left coronary artery ligation, were killed after 24 h, 1 week, 2 weeks and 4 weeks of operation respectively. Left ventricular structure was observed by HE staining, Messon staining was used for the determination of collagen volume fraction (CVF), TUNEL was used for detection of apoptotic cells, radioimmunoassay was used for cardiac AngⅡ and Ald contents and reverse transcriptase-polymerase chain reaction (RT-PCR) for genes expression of collagen type 1 and collagen type 3. Results The infarction sizes were 24%-33%. From 7 days to 28 days after operation, the apoptotic cells and the apoptotic index increased, the Ang Ⅱ level increased gradually (p<0.05～0.001), collagen type 3 mRNA grey level was significantly higher in MI group (p<0.05). From 14 days to 28 days after operation, the CVF increased gradually along with the course of infarction (p<0.05～0.01), ALD level increased gradually and collagen type 1 mRNA grey level was markedly higher in MI group (p<0.05～0.01). Conclusions ①Apoptosis happened in non-infarct zone 14 days after MI in rats. ②There was interstitial fibrosis in non-infarct zone 14 days after MI in rats. ③The interstitial fibrosis might be associated with activation of cardiac RAAS. ④The apoptosis of cardiocytes in non-infarct zone might be related with the excess deposition of interstitial collagen.