Unless damaged by injury or disease, these organs may be used by another individual through transplantation. As long as the heart has oxygen, it continues to work. The ventilator provides enough oxygen to keep the heart beating for several hours. Without this artificial help, the heart would stop beating. Coma is a decrease in brain function, and there is a chance a person may regain consciousness.
Brain death is the irreversible absence of all brain function.
There is no chance of recovery with brain death. However, sometimes television dramas perpetuate myths that people who've been declared dead from severe brain trauma can suddenly awaken and recover completely. In real life, that never happens. No brain dead person has ever regained consciousness. In cases in which a patient does re-awaken, he was never actually brain dead.