What prevents back flow of blood inside the heart during contraction?

(1)Valve prevent backside flow of the blood.
(2)You must know that valves ensure that blood does not flow backwards when the atria or ventricles contract.
(3)Similarly, atrioventricular (AV) valve between atrium and ventricle directs the flow of blood and prevents any backflow into atria.
(4)Semilunar valves, which is present between ventricles and their attached vessels, serve to prevent the backflow of blood to ventricles from their respective attached vessels.