Coloured 3D computed tomography (CT) scan of a healthy heart, lungs (yellow and green) and tracheo-bronchial tree (purple, centre). The heart is a hollow sac of muscular tissue that pumps blood around the body. The aorta (red) carries blood to the body. To the left of the aorta is the upper part of the vena cava vein (blue). 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.