Generally, in the absence of timely treatment, brain death occurs when the heart stops beating for 4 to 6 minutes. Brain death refers to the irreversible termination of all brain functions, including brainstem functions. Deep coma, cessation of spontaneous breathing, and disappearance of brainstem reflexes are the basis for clinical diagnosis of brain death in China. When the heart stops beating, it stops supplying blood and oxygen to the brain and other important organs, and if it is not treated in a timely manner after 4 to 6 minutes, cerebral electrical activity will stop until brain death occurs. It is important to note that effective cardiopulmonary resuscitation (CPR) can be given when the heart stops beating in order to avoid brain death. If there is any serious physical discomfort, medical treatment should be sought promptly.