The timing of surgical intervention in asymptomatic patients with severe degenerative mitral regurgitation (MR) remains controversial. The benefit of early surgery has been suggested in prospective, observational studies, whereas a watchful waiting strategy seemed to be safe and effective in the other prospective study. The consensus guidelines for the performance of early surgery in asymptomatic patients with severe MR are different, reflecting controversy. 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. Thus, the investigators try to compare long-term outcomes of early surgery with those of a conventional-treatment strategy in a large prospective cohort of asymptomatic patients with severe degenerative MR using a propensity analysis, and to identify high-risk subgroups to whom early surgery is more beneficial.