My friend has 6 stents a pacemaker defibulator and the back of his heart is dead. How can someone live with their heart half dead?

Slowly. The heart is a muscle, and uses electricity to generate the "squeeze" necessary to get blood to the whole body. Stents keep blood flowing to the muscle, and a pacer/defibrillator keeps the electricity on and timed right. When part of the heart is dead, patients are less active. They also may develop congestive heart failure, with fluid backing up into lungs. Pills can help.