Heart stopping. During open heart surgery the heart is usually stopped so that the surgeons can attach the bypass grafts to the heart, or to repair or replace a valve. They can stop the heart because the patient is placed on a bypass machine to keep the blood pumping while the surgeons work on the heart. There are now some techniques now that will allow surgeons to perform surgery without stopping the heart.
Can control. Anesthesiologists can make your heart rate whatever they want.