What prevents backflow of blood inside the heart during contration ?

What prevents backflow of blood inside the heart during contraction ?

What prevents backflow of blood inside the heart during contraction ?

Oxygen-rich blood from the lungs comes to the thin-walled upper chamber of the heart on the left. The left upper chamber (A) then relaxes. It then contracts and the blood is allowed to enter the next chamber (B), as it expands. When the muscular left lower chamber of heart contracts the blood is pumped out to the body via aorta. Deoxygenated blood reaches from the body to the upper chamber on the right side of heart (C) and it expands. As this part contracts, the corresponding lower chamber (D) dilates. This transfers the blood to right ventricle, which in turn pumps it to the lungs for oxygenated. What prevents backflow of blood inside the heart during contraction?

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

What prevents clotting of blood inside the blood vessels?

What prevents clotting of blood inside the blood vessels?