The mitral valve is also known as the left atrioventricular valve, or ‘cappuccino valve’. It is attached to the left fibrous atrioventricular ring and is formed by the folds of the endocardium. There are two heart valves, with the anterior one being the anterior尖瓣, larger and commonly called the large valve, which is the junction of the inflow and outflow channels of the left atrium; the posterior one is the posterior尖瓣, smaller and commonly called the small valve.

The heart valves are triangular in shape, with the apex facing the left ventricular cavity. The bottom edges of the two valves often combine with each other, and sometimes there are small accessory flaps between the two halves. The apex, edges, and ventricular surface have many tendons connecting to the papillary muscles. When the atrium contracts, the mitral valve closes the atrioventricular orifice tightly, preventing the backflow of blood into the left atrium.

The left atrium constitutes the majority of the heart, with four passages and one entrance and exit. On both sides of the posterior wall of the left atrium, there are pairs of pulmonary veins orifices, which are the passages for the superior and inferior pulmonary veins; the anterior inferior part of the left atrium has the left atrioventricular orifice, leading to the left atrium. The left atrium has two orifices, the entrance and exit. The passage is the left atrioventricular orifice, surrounded by the left atrioventricular valve (mitral valve), which is also called the anterior valve and posterior valve according to the location; they also have tendons connecting to the anterior and posterior papillary muscles. The entrance and exit are the pulmonary artery orifice, located on the left anterior superior side of the left atrioventricular orifice, surrounded by a crescent-shaped aortic valve membrane.

The mitral valve resembles a ‘single-sided pivot plate’, ensuring that the blood circulation system flows from the left atrium to the left atrium direction and according to a certain total flow rate. When the left atrium contracts, it compresses the blood in the chamber, and the blood impacts the heart valve. When the mitral valve closes, blood does not flow back into the left atrium. The left atrium has a pulmonary artery orifice on its left anterior superior side, and the blood in the left atrium is thus sent into the pulmonary artery. The left atrium is responsible for the transportation of blood throughout the body, so the muscle layer of the left atrium is more developed than that of the right ventricle, about three times thicker than the wall of the right ventricle. The pulmonary artery orifice of the left atrium also has a three-lobed valve, known as the aortic valve membrane. It serves to prevent the backflow of blood from the pulmonary artery into the left atrium.