Cardiac arrest occurs when the heart stops beating. This can be caused by a heart attack in which the heart's demand for oxygen is not met and the heart muscle begins to die. The sudden failure of normal circulation of blood due to failure of the heart to contract results in the body not getting enough oxygenated blood. This causes cells to start to die from oxygen starvation. Cerebral (lack of oxygen to the brain) makes a person lose consciousness and stop breathing, and this makes the heart stop completely. Unless the person is in hypothermia, usually occurs after three to five minutes. (In some cases, the person is put into hypothermia on purpose, to help the person recover better with less damage.)
Cardiac arrest is a medical emergency that, in certain groups of patients, can be reversed if it is treated early enough. When cardiac arrest leads to a person's death, this is called sudden cardiac death (SCD). First aid treatment for cardiac arrest usually begins with cardiopulmonary resuscitation (CPR) to keep oxygenated blood flowing until medical treatment is available.