Heart bypass surgery. Image 3 of 3. Harvested leg vein in a foil cup ready for use in coronary artery bypass graft (CABG) surgery. The vein came from the patient's own leg, and will be attached to the heart to reroute blood around a blockage of a coronary artery. The coronary arteries are the small arteries that supply blood to the heart muscle, and a blockage can be fatal. The blockage is usually a build up of fatty cholesterol. For a sequence showing the preparation of a harvested vein, see images M560/421-423.