Heart bypass surgery. Image 2 of 7. Starfish heart positioner (blue and white machine, right) being used to hold a heart upside down during coronary artery bypass graft (CABG) surgery. A metal retractor is used to keep the chest open. CABG is used to treat stenosis (narrowing) of coronary arteries. An artery or vein, taken from the chest or leg is grafted onto the blocked artery, restoring blood flow to the heart. Coronary arteries can become blocked by a build-up of fatty plaque, leading to loss of blood flow, and consequently a lack of oxygen, in an area of the heart. This can cause heart pain (angina) or a myocardial infarction (heart attack).