Heart bypass surgery. Image 5 of 7 . Surgeon pouring saline over the heart of a patient after coronary artery bypass graft (CABG) surgery. The metal bars are part of the retractor used to keep the chest open during surgery. 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. Blocked arteries can cause heart pain (angina) or a myocardial infarction (heart attack), which may be fatal. For a sequence showing CABG surgery see M560/451 to M560/457.