Abstract: Atrial fibrillation is a common clinical arrhythmia, which could aggravate the rheumatic mitral valve stenosis. The pathomechanism for the mitral valve with atrial fi brillation includes the destruction of the structures of extracellular matrix and the deposition and disproportion of collagen. Matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs)are the main enzymes that affect the extracellular matrix's metabolism. The disequilibrium between MMPs and TIMPs with atrial fibrillation make the extracellular matrix of atrial muscle degradation, typeⅠandⅢcollagen deposition and disarrangement.According to current findings, matrix metalloproteinase 9 and tissue inhibitor of metalloproteinase 2 are the most significant indicators in their terms. This study re fl ects that atrial fi brillation will aggravate the rheumatic mitral valve stenosis by analyzing the relationship between the abnormal expression of MMP 9 and TIMP 2.