Cardiac arrest refers to the loss of heart function. In many cases, it is an expected outcome to a serious illness. Cardiac arrest often results in death.

• "Sudden cardiac arrest" refers to the heart unexpectedly stopping activity due to a potentially reversible cause. Brain death occurs within a few minutes if the situation is not reversed.
• "Sudden cardiac death" refers to an unexpected, heart-related death within 1 hour from the start of symptoms.

Causes of cardiac arrest include:

• Ventricular fibrillation —a rapid, irregular heart rhythm preventing any circulation of blood (most common cause of sudden cardiac arrest)
• Ventricular tachycardia —a rapid but regular heart rhythm that, if sustained, may turn into ventricular fibrillation
• Dramatic slowing of heart rate due to failure of its pacemaker or severe heart block (interference with electrical conduction)
• Respiratory arrest
• Choking or drowning
• Electrocution
• Hypothermia
• Sudden loss of blood pressure
• Unknown causes

A risk factor is something that increases your chance of getting a disease or condition.

Risk factors for cardiac arrest include:

• Coronary artery disease
• Heart attack
• Cardiomyopathy
• Enlarged heart
• Congenital heart disease
• Improperly functioning heart valves
• Conditions affecting the heart's electrical system
• Severe metabolic imbalances
• Adverse drug effects, such as from drugs to treat abnormal heart rhythms
• Lung conditions
• Trauma to the chest
• Extensive blood loss
• Excessive overexertion in people with heart disorders
• Use of illicit substances (eg, cocaine )

Symptoms include:

• Loss of consciousness
• No breathing
• No pulse

Prior to cardiac arrest, some patients report the following symptoms or warning signs in the weeks before the event:

• Chest pain
• Weakness
• Pounding in the chest
• Feeling faint

The first person to respond to a cardiac arrest should check if the person is responsive. Shake the shoulders and ask, "Are you OK?"

• If there is no response, call 911.
• If there are other people around and you can perform CPR (cardiopulmonary resuscitation), send someone to call 911 and turn your attention to the victim.
• Check if the person is breathing. Tilt the head back to open the airway. Put your cheek near the person's mouth and nose. Look, listen, and feel for air movement. If no air movement is detected, CPR should be started.

Prompt treatment improves the chance of survival. The four steps in the cardiac chain of survival are:

Immediately call for emergency medical support. Call 911 as soon as you notice cardiac warning signs or suspect a cardiac arrest has occurred.

CPR helps keep blood and oxygen flowing to the heart and brain until other treatment can be given. The heart and brain are very susceptible to low oxygen levels. Permanent damage can occur, even with successful resuscitation.

During CPR, the rescuer positions the head to open the airway, breathes air into the patient, and compresses the patient's chest.

Once on the scene, emergency medical technicians or paramedics will assess the heart rhythm and determine whether the rhythm warrants defibrillation (eg, ventricular fibrillation or tachycardia). Defibrillation sends an electrical shock through the chest. The surge of electricity aims to stop the ineffective, irregular heart rhythm. This may allow the heart to resume a more normal electrical pattern. Automated external defibrillators check the heart rhythm before instructing the rescuer to give the shock.

Paramedics at the scene and doctors at the hospital provide essential medical care and intensive monitoring. They will give drugs, insert a tube to maintain an open airway, and manage emergency care. Epinephrine is often given early to make the heart more receptive to electrical impulses and improve blood flow to the heart and brain. The patient will receive oxygen. Even if an effective heart rhythm is restored, low oxygen levels may cause serious complications, including damage to the heart, brain, and other vital organs. The emergency medical personnel may perform an electrocardiogram (ECG, EKG)—a test that records the heart's activity by measuring electrical currents through the heart muscle.

Doctors will attempt to find and correct the underlying cause of the cardiac arrest. At the hospital, the doctor will ask about symptoms prior to the collapse and the patient's medical and drug history.

If the patient survives, the doctor will:

• Assess the electrocardiogram.
• Perform a physical exam.
• Confirm a cardiac arrest has occurred.
• Look for the cause.
• Evaluate the effects of pre-hospital care.
• Order additional blood and diagnostic tests to help determine the cause of the arrest.

A telemetry machine will continually monitor the heart's electrical activity.