Background: The incidence of myxomatous mitral valve is increasing in Korea. Transforming growth factor-棺1(TGF-棺1) increased 慣-smooth muscle actin(慣-SMA) production by activating cardiac myofibroblast in vitro. However,in human myxomatous valve the relation between TGF-棺1 and 慣-SMA has not been elucidated.Methods: We classified the 27 subjects into two groups;1)myxomatous degeneration(M:F=11:12,Mean age=55짹15yrs), 2)rheumatic degeneration(M:F=3:1, Mean age= 41짹17yrs) according to the echocardiographic findings.The echocardiographic criteria for myxomatous valve were 1)thick leaflets���3mm, 2) redundant leaflet-motion, 3)echo-density lower than that of the aortic walls. Samples were analyzed by immunohistochemical stain using polyclonal rabbit anti-human antibody to TGF-棺1 and monoclonal mouse anti-慣-SMA antibody. The positively stained areas were measured by using an image analysis program(Image Pro-Plus 4.5) and the TGF-棺1 volume fraction (TGF-VF) and 慣-SMA volume fraction (慣-SMA-VF) were calculated. Results:1.The TGF-VF was 2759짹2294 in myxomatous valve and 864짹276 in rheumatic valve(p=0.04). 2.The 慣-SMA-VF was 4122짹2275 in myxomatous valve and 2421짹844 in rheumatic valve(p=0.002). 3. There was significant correlation between TGF-棺1 and 慣-SMA in myxomatous valve(r=0.38,p=0.04). 4.There was no significant correlation between TGF-棺1 and 慣-SMA in rheumatic valve(r=-0.50, p=0.67).Conclusion: The activation of TGF-棺1 increases the expression of 慣-SMA in myxomatous valve.