Which valve prevents blood from flowing back into the right atrium when the right ventricle contracts?

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

Answer: (C)

During right-heart contraction, the valve between the right atrium and right ventricle acts as a one-way door to keep blood moving toward the lungs. This tricuspid valve closes as the ventricle contracts, preventing blood from flowing back into the right atrium. That unidirectional flow is crucial because the right ventricle pushes blood into the pulmonary artery while the atrium should only supply blood to the ventricle when the heart is relaxed. The other valves have different roles: the pulmonary semilunar valve sits between the right ventricle and the pulmonary artery and prevents backflow into the ventricle, the aortic semilunar valve does the same on the left side, and the mitral valve sits between the left atrium and left ventricle.