Traditional heart surgery uses a "heart-lung" machine to do the work of the heart and lungs. With the patient on the heart-lung machine, the surgeon can stop the beating of the heart and perform surgery.
In off pump bypass surgery, special devices are used to stabilize the heart, and the surgeon can access this part of the heart without motion. The surgeon can then bypass the affected portion of a native coronary artery with a graft from a vein or artery.

