<unk>  is a sudden loss of blood flow throughout the body resulting from the failure of the heart to pump effectively. It is a rapidly fatal medical emergency requiring immediate intervention with<unk> rdiopulmonary resuscitation (CPR) until further treatment<unk> n be provided.<unk>  results in rapid loss of consciousness and breathing may be abnormal or absent. While<unk>  may be<unk> used by heart attack or heart failure, these are not the same, and in 15 to 25% of<unk> ses there is a non-cardiac<unk> use. Some individuals may experience chest pain, shortness of breath or nausea immediately before entering<unk> . Additionally, an elevated heart rate and feelings of light-headedness may occur before the episode. If not intervened by CPR and defibrillation,<unk>  typically leads to death within minutes. The most common<unk> use of<unk>  is an underlying heart problem like coronary artery disease which decreases the amount of oxygenated blood supplying the heart muscle. This, in turn, damages the structure of the muscle, which<unk> n alter its function. These changes<unk> n over time place the patient's heart in ventricular fibrillation (V-fib) which most commonly precedes<unk> . Less common<unk> uses include major blood loss, lack of oxygen, very low potassium, heart failure, inherited heart arrhythmias and intense physical exercise.<unk>  is diagnosed by the inability to find a pulse. CPR and defibrillation<unk> n reverse a<unk> , leading to Return-of-Spontaneous-Circulation (ROSC), but without such intervention it<unk> n lead to a certain death. In some<unk> ses,<unk>  is an anticipated outcome of serious illnesses where death is expected. Treatment for<unk>  includes immediate CPR and, if a shockable rhythm is present, defibrillation. Two protocols have been established for CPR: basic life support (BLS) and advanced<unk> rdiac life support (ACLS). Among those whose pulses are reestablished, targeted temperature management may improve outcomes. In addition, the<unk> re team may initiate measures to protect the patient from brain injury and preserve brain function. In post-resuscitation<unk> re, an implantable<unk> rdiac defibrillator may be considered to reduce the chance of death from recurrence. In the United States, approximately 535,000<unk> ses occur a year. About 13 per 10,000 people (326,000 or 61%) experience<unk>  outside of a hospital setting, while 209,000 (39%) occur within a hospital.<unk>  becomes more common with age and affects males more often than females. The percentage of people who survive out-of-hospital<unk>  with treatment by emergency medical services is about 8%. However, fictional media in the U.S. has often portrayed the immediate survival rate of<unk>  to be unreasonably high. This may contribute to misinformed expectations of the resuscitative efforts from the general public with many studies showing the expected survival rate of resuscitative efforts after<unk>  exceeding 40–50%. These portrayals may also contribute to a patient's or medical decision maker's desire to pursue aggressive measures. When given accurate information, it has been shown that many are less likely to choose resuscitation when critically ill. In the event that<unk> rdiopulmonary resuscitation is successful, complete recovery is not guaranteed as many survivors experience an array of disability including partial paralysis, seizures, difficulty with walking, speaking, or memory, limited consciousness, or persistent vegetative state and brain death.
Cardiac arrest
Respiratory arrest
Spinal shock
Syncope 
Permissive hypotension
Heat syncope
Sleep paralysis
Traumatic cardiac arrest