Answer:-The ventricles of the heart have thicker muscular walls than the atria. This is because blood is pumped out of the heart at greater pressure from these chambers compared to the atria. The left ventricle also has a thicker muscular wall than the right ventricle, as seen in the adjacent image.
Each side of the heart has an atrium that receives blood from elsewhere in the body and a ventricle that pumps the blood out of the heart
Semilunar valves in the arteries prevent back flow of blood from the arteries into the ventricles. Why are the walls of the atria thinner than the walls of the ventricles? This is because their contractions don't need to be that powerful as the blood only needs to travel down a short distance to the ventricles. Deoxygenated blood enters the heart at the right atrium via the superior vena cava (vein), then travels into the right ventricle which pumps the blood out to the lungs via the pulmonary trunk (artery). After oxygenation, the blood travels back to heart via the pulmonary veins and enters the left atrium.