Which valve prevents blood from flowing back into the left ventricle?

• A. Mitral Valve
• B. Aortic Valve
• C. Pulmonary Valve
• D. Tricuspid Valve

Answer: (B)

Valves keep blood moving in one direction, each at its specific outflow or inflow boundary. The left ventricle pumps into the aorta through the aortic valve, a semilunar valve at the LV outflow. When the ventricle relaxes, the pressure in the aorta can push back toward the ventricle, so the aortic valve closes to prevent any backflow. The other valves serve the opposite directions: the mitral valve blocks blood from moving from the ventricle back into the left atrium, the tricuspid blocks backflow into the right atrium, and the pulmonary valve blocks backflow into the right ventricle. Therefore, the valve preventing backflow into the left ventricle is the aortic valve.