Coronary Artery Bypass Surgery or CABG is a surgical procedure performed to restore the blood supply to sections of heart that have reduced or no blood supply.
The blockage or obstruction in the vessels is caused due to depostion of fat in the walls of the arteries and this gradual process is called atherosclerosis or arteriosclerosis. Obstruction leads to angina pain or death of heart muscles (also called myocardial infarction) and causes a 'heart attack'.