Foetal heart, illustration. The heart is a hollow sac of muscular tissue that pumps blood around the body. The two left chambers, the upper atrium and lower ventricle are shown in section. The aorta (red) carries blood to the body. To the left 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 (below the aorta). Illustration from Traite d' Anatomie humaine By L. Testut (1905) Paris.