What happens during heart bypass surgery?

Open Heart Surgery. Patients are placed on a heart lung machine to support their respirations and circulation while new blood vessels (arteries and veins) are grafted onto the hear to "bypass" areas that are blocked.
Varies... For many years bypass involved an incision down the middle of your chest, splitting the sternum, stopping the heart and going on the heart-lung machine, and then performing the bypass. Now, some surgeons use other incisions and may not split the sternum. Some people do bypasses without stopping the heart or using the bypass machine. Some use robotics to perform the surgery.