Which valve prevents backflow from the aorta into the left ventricle?

• A. Mitral valve
• B. Pulmonary semilunar valve
• C. Tricuspid valve
• D. Aortic semilunar valve

Answer: (D)

Blood moves through the heart in one direction thanks to the semilunar and atrioventricular valves. The valve between the left ventricle and the aorta is the aortic semilunar valve. It opens to let blood be ejected into the aorta during ventricular contraction and then closes as the ventricle relaxes, preventing blood from flowing backward from the aorta into the left ventricle. The other valves sit elsewhere: the mitral valve sits between the left atrium and left ventricle, the tricuspid between the right atrium and right ventricle, and the pulmonary semilunar valve between the right ventricle and the pulmonary artery. Therefore, the valve preventing backflow from the aorta into the left ventricle is the aortic semilunar valve.