Illustration of the heart seen from the left. The heart is a hollow sac of muscular tissue that pumps blood around the body. The aorta (curved, top centre) carries blood to the body. Three smaller arteries are seen branching off it. Deoxygenated blood is returned from the body and travels from the heart to the lungs (where it obtains oxygen) and back to the heart through the pulmonary artery (below the aorta).