Objective To investigate the effect of ischemia and ischemia/reperfusion(I/R) in rat heart on Matrix metalloproteinase-1(MMP-1). Methods The I/R animal models were established by shutting down and reopening the anterior interventricular branch with a silver clamp,then the distribution and amount of MMP-1 of the normal and I/R rat hearts were observed by immunohistochemical staining and Western blotting and analyzed by computer image analysis. BR>Results 1. Immunohistochemical staining showed MMP-1 existed mainly in the cardiac matrix.There were strong positive reactions in fibrocytes, smooth muscle cells of the blood vessel and endothelial cells of capillaries.MMP-1 didn’t show distinct changes 30 minutes after ischemia,while its concentration increased dramatically 60 minutes after ischemia.The positive reaction of MMP-1 increased 30 minutes after I/R,and 60 minutes after I/R there was large fusion areas in MMP-1 existing regions. 2. Quantitative analysis showed no dramatic changes of MMP-1 after ischemia for 30 minutes(P>0.05),while dramatic changes were seen 60 minutes after ischemia(P<0.05).MMP-1 changed dramatically 30 minutes and 60 minutes after I/R. 3. Western blotting showed that there were no distinct naked-eye-observable changes.The bands of MMP-1 became widened 30 minutes after I/R, and became obviously widened 60 minutes after I/R.Conclusion 1. MMP-1 is secreted by fibrocytes,smooth muscle cells and endothelial cells of cardiac tissue under physiological conditions,and cardiomyocytes has the potential to secrete MMP-1 under ischemia or I/R. 2. The longer time the heart ischemia lasts,the greater MMP-1 concentration will increase.Reperfusion can increase MMP-1 concentration to an even higher level,which may be the main cause of the collagen destruction after heart I/R. BR>