Heart after surgery. Coloured X-ray of the chest of an elderly woman after open heart (cardiac) surgery. Open heart surgery may be conducted for coronary artery bypass in which a healthy artery is used to reroute the blood from a blocked coronary artery due to atherosclerosis (fatty build-up inside blood vessels). Cardiac surgery may also be conducted to fit a new heart valve, or to fit a stent to support a damaged blood vessel of the heart. The heart is seen at lower centre; sutures (green strings) stitching the chest closed from the operation are seen; round electrodes on the skin monitor the heartbeat. The lung fields on either side of the heart are opaque due to fluid build-up in the lungs; this occurs in congestive heart failure.