Open heart surgery differs from other surgeries in that it literally involves cracking open the chest.
Many different surgeries are conducted in an open-heart schematic. 'Open heart' is a misnomer; the chest cavity is usually the open part.
The open heart procedure was first performed by Dr. John Heysham Gibbon in 1953 at the University of Pennsylvania using an oxygenator. Subsequent attempts failed, but following the invention of the heart-lung machine , open heart surgeries had a higher rate of success - modern surgeries are occasionally conducted using a beating heart which is stabilized physically and chemically .
All surgeries in which the heart does not beat are bypass operations, in which a heart-lung machine is used to keep the patient living during surgery. Most operations are conducted in this sort of manner:
Surgeons make an incision down the sternum, in both skin and fat, before retracting the skin. They cauterize using an instrument called a bovie, which minimizes the loss of blood, vital to keeping the patient alive since much blood is lost during the operation. A bone-saw is used to cut the sternum in half, and the ribs are retracted to expose the heart under the pericardium, which is a membrane around the heart. The surgeon inserts a large cannula in the aorta and vena cava, bypassing the heart, then cools the heart with saline ice slush and occasionally injects it with potassium, rendering the patient biologically dead. From this point, the surgeon does what he will with the heart, replacing it, bypassing it, or repairing it. The heart is started using an on-heart AED, the cannulae are removed, the aorta and vena cava are repaired, the ribs are wired together, and the skin is closed.
Frequent side effects include death, stroke, postperfusion syndrome due to neurological damage, and psychological problems such as depression or anxiety.
Source: Wikipedia, WebMD, NIH