Introduction LA volume provides the significantly prognostic information in the general population and patients with heart disease, including acute myocardial infarction, left ventricular dysfunction, mitral regurgitation, cardiomyopathy and atrial fibrillation. Large LA volume, which represents chronic diastolic dysfunction, is associated with poor outcome, regardless of systolic function. Thereby, LA volume provides a long-term view of whether or not the patient has the disease of diastolic dysfunction, regardless of whatever loading conditions are present at the time of the examination, as the hemoglobin A1C in diabetes mellitus. Until now, the relation between LA volume and LV filling pressure confirmed directly by simultaneous echocardiography-catheterization is sparse. This study therefore assessed the correlation between LA volume and LV filling pressure in patients with severe mitral regurgitation (MR). As LA pressure rises to maintain adequate LV diastolic filling, increased atrial wall tension tends to dilate the chamber and stretch the atrial myocardium. Therefore, the smaller LA stretchability, the more pressure LA faces. The study is designed to assess 1) the relationship between LV filling pressure and LA distensibility, and 2) the power of left atrial distensibility to predict the prognosis, including operation mortality, the rate of post-operation atrial fibrillation, and late heart failure event in patients with severe mitral regurgitation.