(1) Rheumatic mitral valve insufficiency, the most common cause in China, is more common in men. It is often accompanied by mitral stenosis and aortic valve damage. (2) Mitral leaflet prolapse (e.g., tendon rupture, papillary muscle rupture, degenerative lesions, etc.), which is an increasingly common cause. (3) Coronary artery disease combined with mitral valve insufficiency. (4) Infective endocarditis. (5) Enlarged left ventricle. (6) Congenital heart disease: such as endocardial cushion defect. Clinical manifestations: In general, mild to moderate mitral valve insufficiency has no symptoms or only mild discomfort, which can last for several years to more than 20 years. Common symptoms of moderate-to-severe mitral valve insufficiency include labor dyspnea, fatigue, seated breathing, and a significant decrease in activity tolerance. Hemoptysis and embolism are less common. In advanced right heart failure, liver bruising and enlargement with tenderness, ankle edema, and pleural or ascites may occur. There is no absolute standard. According to the US heart valve surgery guidelines, clinicians often recommend surgery as long as the patient has a moderate degree of closure insufficiency or above and is willing to have surgery; in China, surgery is generally recommended when there is moderate closure insufficiency or above, combined with chest tightness, weakness, swelling, atrial fibrillation and other symptoms, or when the heart ultrasound indicates significant enlargement of the left atrium. Drug therapy alone is not sufficient for mitral valve insufficiency above moderate level. How is mitral valve insufficiency treated? There are two treatment methods for mitral valve insufficiency: mitral valvuloplasty and mitral valve replacement. The success rate of mitral valvuloplasty is more than 80% in hospitals with high technical level, including edge technique, gliding technique, artificial tendon technique, annular reduction technique, and tendon transfer technique. However, mitral valvuloplasty is inappropriate when combined with severe leaflet destruction (e.g., endocarditis) or stenosis (mitral stenosis). The advantage of mitral valvuloplasty is that the patient does not have to take warfarin (anticoagulant medication) for life. The second is valve replacement, which is available in general hospitals and is very effective, with the main disadvantage of lifelong anticoagulation. What about mitral valve insufficiency in infants and children? Most of the time, this is one of the combined disorders of other heart diseases or one of the complications of other cardiac surgeries, which usually requires mitral valvuloplasty treatment and has a high success rate.