Abstract: Objective:To investigate the effect of captopril on collagen type Ⅰ and type Ⅲ and their mRNA expressions in abdominal aortic banding model rats.Methods:Myocardial fibrosis rat model was established by partially banding abdominal aorta with silver clip (inside diameter 0.7 mm) according to Doering's method.Optical density values of collagen typeⅠand type Ⅲ were measured by immunohistochemistry staining after 8 weeks.The mRNA expressions of collagen typeⅠand type Ⅲ were analyzed by real-time PCR amplification.Results:In the 8th week,compared with sham operation group,the average optical density value and mRNA expressions of collagen type Ⅰ and type Ⅲ were increased obviously in model group (P<0.01).The immunohistochemistry staining displayed that collagen type Ⅰand type Ⅲ were deposited,thicken and confused in myocardium stroma;and the quantity of collagen was decreased obviously in model group.Conclusions:The quantity of collagen type Ⅰ and type Ⅲ and the related mRNA expressions were increased in myocardical fibrosis induced by abdominal aortic banding in rats;captopril could delay even reverse the process of myocardial fibrosis.