A) Aortic semilunar valve B) Mitral (bicuspid) valve C) Tricuspid valve D) Pulmonary semilunar valve 1) Prevents backflow into the left ventricle. ----------------- 2) Prevents backflow into the right atrium. -------------------- 3) Prevents backflow into the left atrium. --------------------- 4) Prevents backflow into the right ventricle. ------------------------- 5) Atrioventricular (AV) valve with two flaps. ----------------- 6) Atrioventricular (AV) valve with three flaps. ------------------------

The four heart valves of our heart have two main functions. They open to allow blood to pass through them, and close to prevent blood from going back (backflow).

Semilunar valves:

There are two semilunar valves and they have 3 cusps. They open up to areas outside the heart. Their main function is to prevent backflow towards the heart.

a. Aortic semilunar valve is located in between the Aorta and the left ventricle. It opens up to the Aorta where oxygen-rich blood leaves the heart and go towards the other parts of the body. It prevents backflow to the left ventricle.

b. Pulmonary semilunar valve is located in between the right ventricle and the pulmonary artery. It opens up to the pulmonary artery which carries unoxygenated blood towards the lungs. It prevents backflow to the right atrium.

Atrioventricular valves:

They are named as such because they are found in between the atria and the ventricles.

a. Tricuspid valve has three cusps and it is found on the right side of the heart. It is located in between the right atrium and the right ventricle. It prevents backflow to the right atrium.

b. Mitral valve has 2 cusps and that is why it is also known as the bicusip valve. It is located in between the left atrium and the left ventricle. It prevents backflow to the left atrium.