The heart chamber with the thickest muscle wall is the left ventricle. Ventricles are the lower two chambers, whereas the atria are the upper two chambers of the heart. The two ventricles have thicker muscular walls than the two atria.
The atria receive blood from the veins. When they contract, blood transfers from the atria to the ventricles, so the atria do not need to be as muscular as the ventricles.The ventricles of the heart have thicker muscular walls because they pump blood throughout the body. The pressure created in the ventricles causes blood to rush into the large arteries of the body such as the aorta and the pulmonary artery. The left ventricle is twice as muscular as the right because it has to do more work by pumping blood to all the organs of the body. In contrast, the right ventricle only pumps deoxygenated blood to the lungs, which are a short distance away.