The heart has four valves that separate its chambers. There is a valve between each atrium and ventricle, and a valve at the outlet of each ventricle.[9]
The valves between the atria and ventricles are called the atrioventricular valves. Between the right atrium and the right ventricle, the valve is called the tricuspid valve, as the valve has three leaflets,[22] connected by tendon cords to three anterior, posterior, and septal papillary muscles, and their name came according to their position.[22] While the valve between the left atrium and the left ventricle is called the mitral valve, and it is also called the bicuspid valve, because it has two leaves, anterior and posterior, which are linked by tendinous cords to the papillary muscles that emerge from the walls of the ventricle.[23]
The papillary muscles extend from the walls of the heart to the valves via cartilaginous connections called chordae tendinae. These muscles prevent the valves from retracting too far when they are closed.[24] During the diastolic phase of the cardiac cycle, the papillary muscles are also relaxed, and when the chambers of the heart contract, the papillary muscles contract as well. This creates pressure on the chordae tendinae that helps keep the valve leaflets in place and prevents them from turning into the atria.[9] [A][22]
There are two other semilunar valves located at the outlet of each ventricle. The pulmonary valve is located at the base of the pulmonary artery. This valve has three leaflets, but they are not associated with papillary muscles. When the ventricle relaxes, blood returns to the ventricle from the artery, and this return fills the valve pockets that press the valve leaflets to close and thus block the valve mouth. The aortic semilunar valve is also located at the base of the aorta. The valve leaflets are not attached to papillary muscles, as is the case in the pulmonary valve. It also has three leaflets that close due to the pressure of blood returning from the artery towards the ventricle [9].
