Illustration of the heart seen from the rear. 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. To the right of the aorta is part of the vena cava vein. This vein carries deoxygenated blood into the heart from the body. This blood then travels from the heart to the lungs (where it obtains oxygen) and back to the heart through the pulmonary artery (left of the aorta).