Which valve prevents blood from flowing back into the heart after it has been pumped out?

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

Answer: (A)

The key idea is that blood leaving the ventricles is kept moving forward by the semilunar valves, which close to prevent any backflow into the heart. The valve between the left ventricle and the aorta—the aortic valve—opens to push blood into the aorta and then closes as ventricular pressure drops and the aorta’s pressure is higher. This closing stops blood from flowing back into the heart from the aorta, ensuring one-way flow into the systemic circulation. The same principle applies to the valve between the right ventricle and the pulmonary artery, but the question’s focus on blood pumped out toward the body points to the aortic valve as the best fit.