The heart stops beating for about 4-6 minutes will lead to brain death of the patient. brain is the most important organ of the human body, glucose and oxygen consumption accounts for about 20%-25% of the whole body supply, but there is almost no reserve of glucose and oxygen in the brain tissue. When the heart stops beating the blood supply to the brain will be interrupted, resulting in the patient’s brain tissue and brain cells being in a stage of ischemia, hypoxia and lack of energy. 2 minutes later the patient’s brain electrical activity will stop, and 4-6 minutes later irreversible damage to the brain tissue will occur and brain cells will be necrotic. Effective cardiopulmonary resuscitation must be given when a patient is in cardiac arrest to avoid brain damage that could lead to brain death. So adequate blood supply to the brain is very important to maintain normal brain function.