Which structure prevents blood from backflow during contraction of the heart?

The structure that prevents blood from backflow during the contraction of the heart is the valves. These are specialized tissue flaps located in the heart that open and close in response to pressure changes within the heart chambers. When the heart contracts, the valves ensure that blood flows in the correct direction—either from the atria to the ventricles or from the ventricles to the arteries—thus preventing any backward flow. This mechanism is essential for maintaining efficient circulation and ensuring that oxygenated blood reaches the body while deoxygenated blood returns to the lungs.

The myocardium, which is the heart muscle itself, is responsible for the contraction of the heart but does not play a role in preventing backflow. The pericardium is a protective sac surrounding the heart, and while it helps anchor the heart in place, it does not regulate blood flow. Finally, coronary arteries supply blood to the heart muscle but do not prevent backflow during cardiovascular contractions. The function of the valves is crucial for the heart's efficiency and overall function within the cardiovascular system.