How many valves are in the heart?

• A. Two
• B. Four
• C. Three
• D. Five

Answer: (B)

Think of the heart as having four valves that carefully direct blood flow. There are two atrioventricular valves between the atria and ventricles—the tricuspid on the right and the mitral on the left—and two semilunar valves at the exits of the ventricles—the pulmonary valve and the aortic valve. These valves open and close with every heartbeat to keep blood moving in the right direction and to prevent backflow. The atrioventricular valves allow blood to move from the atria to the ventricles while the heart relaxes, and they close when the ventricles contract to stop blood from flowing back into the atria. The semilunar valves open when the ventricles contract to push blood into the lungs and the body, and they close when the ventricles relax to prevent arterial blood from flowing back into the heart. So, there are four valves in total.