INTRODUCTION: There are multiple causes of mitral regurgitation. Its etiology 
includes floppy valve, postinflammatory disease, infective endocarditis, and 
other disorders. Recently, there has been an increased tendency to remove only 
portions of the mitral valve, causing difficulty in the determination of 
etiology. Our objective was to study the pathology and etiology of mitral 
regurgitation from surgically removed specimens.
METHODS: Native mitral valve specimens surgically excised due to mitral 
insufficiency were examined. Etiology was determined according to macroscopic, 
microscopic, clinical, and operative findings.
RESULTS: Among 278 mitral valve specimens, 43% were classified as floppy valve, 
31% as postinflammatory disease (presumably associated with rheumatic fever), 
12% as infective endocarditis, and 14% as miscellaneous group. In floppy valves, 
diffuse myxoid change and chordal rupture were the main findings. In 
postinflammatory disease, moderate neovascularization and chronic inflammatory 
cell infiltration were most commonly found. Aschoff bodies were found in two 
cases. In infective endocarditis, gram-positive cocci were found in 70% of 
cases. In the miscellaneous group, three cases were related to Marfan syndrome 
and one case was related to papillary muscle necrosis. In comparison with 
postinflammatory disease, the posterior leaflet in the floppy valve had a 
significantly longer basal free-edge length, a more frequent chordal rupture, 
and an higher mean age of patients. Among completely and partially excised 
specimens with postinflammatory disease, there were no significant differences 
in microscopic findings.
CONCLUSION: The three most common etiologies in mitral regurgitation were floppy 
valve, postinflammatory disease, and infective endocarditis. Macroscopic, 
microscopic, clinical, and operative findings are important in the evaluation of 
etiology, especially in partially excised specimens.