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Heart and lungs. Axial computed tomography (CT) scan of the chest of a 42-year-old woman, showing the normal heart and lungs as viewed from below. The heart (upper centre) is located between the two lungs (left and right). Blood vessels are seen branching out in the lungs. Bone structures include the ribs, the breastbone (sternum) and the backbone (spine). (KEYSTONE/SCIENCE PHOTO LIBRARY/ZEPHYR/SCIENCE PHOTO LIBRARY)