The mitral valve is one of the valves of the heart, which is divided into a left heart and a right heart, each of which is divided into an atrium and a ventricle. The mitral valve is the valve between the left atrium and the left ventricle, which in layman’s terms is equivalent to the door between the left atrium and the left ventricle. The door of the heart is constantly opened and closed throughout the life of the heart, with the movement of diastole and contraction, so that the blood between the two atria and ventricles does not flow backwards and forwards to each other. Some people are born with some abnormalities in the development of the heart and valves that may cause reflux. In some people, mitral regurgitation can be caused by rheumatic heart disease, or by age-related changes in the heart valves that occur when the valves are used for too long. If the regurgitation is a small or moderate amount, it does not cause significant clinical symptoms because the overall blood flow in the heart is still smooth and does not produce eddies or backflow. If there is a large amount of regurgitation, it is equivalent to the loss of mitral valve function, and the blood inside the heart will backflow, which will cause cardiomegaly and heart failure over time, requiring surgical valve replacement treatment.