_______ prevents the backflow of blood in heart.

There are four valves in the heart, which prevent blood from flowing backward in the heart. The valves open easily in the direction of blood flow but when the blood pushes the valve in the opposite direction, the valves close. 2 valves = Atrioventricular valves = located between atria and ventricles 2 valves = Semilunar valves = located between ventricles and arteries. Pulmonary valve - Between the right ventricle and pulmonary artery Aortic valve - Between the left ventricle and aorta