Medical ethics is not without its controversies, yet some doctrines in the field have near-universal acceptance. Three such prevailing beliefs are (1) that donors of vital organs (heart, liver, lungs, and both kidneys) must be dead before organs can be removed for life-saving transplantation; (2) that critically ill and dying patients die of their illnesses once life-sustaining efforts are withdrawn (not from treatment removal); and (3) that individuals exhibiting brain death are dead.