Heart bypass surgery. Image 2 of 3. Surgeon using a syringe to inject saline and test a vein for leaks. The vein was removed from a patient's leg for use in coronary artery bypass graft (CABG) surgery to bypass 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 harvested blood vessel will be attached to the heart, and will reroute blood around the blockage. 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.