There are two sides of the heart and each side (left and right) has two chambers each. The two chambers: atria (top) and a ventricle (bottom). Even though the two sides of the heart have two chambers each, they have very different roles... The left side has a far greater role to play than the right side because the left side pumps the blood to the body. The right side pumps blood to the lungs which is a far shorter distance. Less force is needed to pump to the lungs due to the closer proximity to the heart. Note: (The left ventricle is much thicker than the right ventricle and is responsible for the size difference).