The walls of the ventricles are thicker because the ventricles pump blood under higher pressure over greater distances. The walls of the atria are thicker because the atria receive blood under pressure. The wall of the right ventricle is thinner than that of the left ventricle because the right side of the heart pumps blood a shorter distance at lower pressure. Although the right side of the heart has a smaller workload, the right and left ventricle simultaneously eject the same amount of blood. All of these choices are correct.