Clinical outcome in asymptomatic patients with MR is poorly defined and it is important to identify high-risk patients in whom early surgery may be warranted. Older patients and those with a larger effective regurgitant orifice (ERO) showed increased mortality under medical management, but it is controversial whether early surgery would improve clinical outcome of such patients, because the performance of surgery in high-risk patients might be associated with increased operative risk. Although randomized trials are required to establish indications for early surgery, ethical and financial constraints do not allow us to conduct a randomized trial and the investigators choose to perform a propensity analysis in a large prospective cohort of patients. The investigators try to compare long-term outcomes of early surgery with those of a conventional-treatment strategy that is based on current guidelines in a large prospective cohort of asymptomatic patients with severe degenerative MR using a propensity analysis, and examine the hypothesis that the reduction in cardiac mortality or cardiac event by early surgery is particularly evident among patients aged > 50 years or those with ERO ≥ 0.4 square centimeter.