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

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

• A. Right AV (tricuspid) valve
• B. Aortic semilunar valve
• C. Pulmonary semilunar valve
• D. Left AV (bicuspid/mitral) valve

Answer: (D)

Blood moves through the heart in a one-way path thanks to valves. The valve between the left atrium and left ventricle—the mitral (left AV) valve—opens to let blood flow into the left ventricle during relaxation, then closes as the ventricle contracts to prevent any backflow into the atrium. This closing action specifically stops blood from moving backward from the left ventricle into the left atrium. The other valves regulate flow at other junctions: the tricuspid valve sits between the right atrium and right ventricle, while the aortic and pulmonary semilunar valves prevent backflow from the aorta and pulmonary artery, respectively.

Blood moves through the heart in a one-way path thanks to valves. The valve between the left atrium and left ventricle—the mitral (left AV) valve—opens to let blood flow into the left ventricle during relaxation, then closes as the ventricle contracts to prevent any backflow into the atrium. This closing action specifically stops blood from moving backward from the left ventricle into the left atrium. The other valves regulate flow at other junctions: the tricuspid valve sits between the right atrium and right ventricle, while the aortic and pulmonary semilunar valves prevent backflow from the aorta and pulmonary artery, respectively.