Heart and lungs. Coloured frontal chest X-ray showing a healthy heart (pale area, lower centre to lower right) and lungs (dark). The heart is a hollow, muscular organ that pumps blood around the body. The blood picks up oxygen from the lungs before returning to the heart to be sent to the rest of the body. These organs are protected by the ribs (horizontal bands) and the sternum (white, down centre). Below the heart and lungs is the diaphragm, a muscular sheet that contracts and expands, pulling and pushing air in and out of the lungs.