Assuming it is the human heart in the question above, it is a four-chambered heart with a wall called the septum separating the left and right sides. Each side has its specific function. The right side pumps de-oxygenated blood to the pulmonary arteries in a pathway known as pulmonary circulation. These arteries bring blood to the capillaries inside the lungs. Here, oxygen is absorbed by hemoglobin, the pigment in the red blood cells and carbon dioxide diffuses from the circulating blood into the air sacs to be exhaled. The oxygenated blood travels to the left side of the heart via the pulmonary veins. These bring blood to the left atrium. It travels down to the left ventricle which is the slightly larger of the two ventricles inside the heart. Its function is to pump oxygenated blood to the aorta, the body's largest artery to all parts of the body. This is called systemic circulation. This is accomplished because the aorta begins to branch off into smaller arteries, then capillaries, which can be found in all organs of the body and eventually, diffusion of oxygen occurs between the blood inside the capillaries (the body's tiniest blood vessels) and cells of the body. Capillaries are one-cell thick and oxygen can diffuse through the capillary walls and enter the body cells.