What Is Sudden Cardiac Arrest?

When the Heart Suddenly Stops Beating

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Sudden cardiac arrest is an abrupt loss of heart function that leads a person to suddenly collapse, lose consciousness, and stop breathing. The heart stops beating and blood stops flowing to the brain and other vital organs.

Death can occur in minutes, and almost 90% of cardiac arrests that occur outside of hospitals are fatal. However, survival is possible with a prompt response that includes calling 911, starting CPR chest compressions, and shocking the heart back into rhythm with an automated external defibrillator (AED).

This article explores the most common causes of cardiac arrest in adults and children, how to recognize it, and steps you can take to increase a person's chances of survival.

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"Cardiac" means "heart" and "arrest" means "to stop."

Any time you see the term "arrest" paired up with a body system, it refers to that system ceasing its function. For example, respiratory arrest means the same thing as "not breathing."

Cardiac arrest is different from a heart attack. A heart attack is a blockage of blood flow to the heart muscle, which deprives it of oxygen and damages the heart. Cardiac arrest is an electrical malfunction that causes the heart to stop pumping. However, a heart attack can lead to cardiac arrest.

Causes of Cardiac Arrest In Adults

Looking for causes of cardiac arrest is a little bit like looking for causes of why the car broke down—it's a really large list. Cardiac arrest can be caused by almost any type of heart condition.

Below are some common causes of cardiac arrest in adults.

Cardiac Arrhythmia

By far, the most common cause of cardiac arrest is a cardiac arrhythmia. An arrhythmia is a problem in the heart's electrical communication system that makes the heart beat irregularly.

Types of arrhythmias that can lead to cardiac arrest include:

  • Ventricular fibrillation is when electrical impulses in the ventricles, or lower chambers of the heart, become erratic and ineffective. Ventricular fibrillation is the arrhythmia most commonly responsible for cardiac arrest and is one of the most treatable if quickly corrected.
  • Ventricular tachycardia is when the heart beats too fast, which is typically defined as faster than 100 beats per minute for adults.
  • Bradycardia is when the heart beats too slowly, which is typically below 60 beats per minute for adults.
  • Asystole is an arrhythmia in which electrical activity and pumping of the heart stops. It is known more generally as flatlining due to the flat line on an electrocardiogram, which measures electrical activity of the heart.

A heart that's enlarged or scarred, which can occur with a heart attack or other heart condition, is more prone to arrhythmias that can lead to cardiac arrest.

Bleeding and Shock

Shock is a complicated medical condition with several causes. A simplified version is basically to say shock is really low blood pressure. If the blood pressure gets too low, there won't be a pulse or enough blood flowing to the brain to keep the victim alive.

Electrolyte Imbalances

Electrolytes are important for body chemistry to function correctly. Calcium, sodium, and potassium are the most important electrolytes.

Calcium and potassium have to be in balance—sitting on either side of cell membranes, ready to switch places—in order to cause muscles to contract or nerves to transmit impulses. Once calcium and potassium swap places and cause things to happen, sodium puts them back in their place for the next time.

If there aren't enough of one or two or all of these electrolytes, then the heart muscle cells can't move, which means the heart won't pump. Heat illness (heat exhaustion or heat stroke), kidney failure, and certain types of medications can cause electrolyte imbalances.

Causes of Cardiac Arrest In Kids

Arrhythmias are also a common cause of cardiac arrest in children and adolescents.

Kids don't suffer sudden cardiac arrest as often as adults, but when they do, it is usually due to a structural problem with the heart. The child's family may or may not be aware of the child's heart condition prior to the cardiac arrest.

Structural Abnormalities

Structural abnormalities can lead to cardiac arrest in children. This can include congenital heart disease, a malformation of the heart that is there at birth, and hypertrophic cardiomyopathy, a condition that is often undiagnosed and causes muscle cells in the heart's ventricles, or lower chambers, to thicken.

Hypertrophic cardiomyopathy can lead to arrhythmias, particularly during exercise.


Myocarditis is an inflammation of the heart muscle that can affect its ability to contract normally, which can lead to cardiac arrest. Myocarditis is often caused by infections, such as viral infections or bacterial infections. It can also be due to immune or inflammatory diseases or other causes, such as toxins or allergic reactions.

Genetic Conditions

Some genetic conditions, particularly those that go undiagnosed, can lead to cardiac arrest. Examples include:

  • Long QT syndrome is a disorder of the heart's electrical system that can cause a fast and chaotic heart rhythm.
  • Wolff-Parkinson-White syndrome causes an extra electrical pathway that can lead the heart to pump too fast.
  • Marfan syndrome is a connective tissue disorder that can lead to tears in the heart's aortic blood vessel. Individuals with this genetic condition tend to be tall.

Commotio Cordis

Very rarely, cardiac arrest caused by ventricular fibrillation occurs due to a strike to the chest in children; this is called commotio cordis. For example, it can occur from a baseball or hockey puck hitting the chest.

How to Help Someone in Cardiac Arrest

To improve the odds of survival for someone who collapses in cardiac arrest, the American Heart Association lists six important steps:

  • Recognizing cardiac arrest (a person has collapsed and is unconscious) and calling 911
  • Quickly starting CPR focusing on chest compressions
  • Using an AED as quickly as possible
  • Resuscitation by emergency medical services or other healthcare providers
  • Post-cardiac arrest medical care
  • Recovery that includes additional treatment, observation, rehabilitation, and psychological support

AEDs have pads with sensors that are put on the chest to analyze the heart rhythm and deliver an electric shock to restart the heart if the device indicates it is needed. AEDs are portable devices found in many public buildings, offices, and sports facilities that are intended for public use.

Research shows that the chance of survival from cardiac arrest doubles when a bystander steps in to use an AED before emergency responders arrive, according to research in the journal Circulation. Plus, every minute counts. The chance of survival decreases by 7% to 10% for every minute that passes without AED use.

If someone collapses in cardiac arrest, call 911, start CPR, and use an AED if it's available.


Sudden cardiac arrest is a life-threatening emergency that causes an abrupt loss of heart function. It is usually fatal when it occurs outside of a hospital but a prompt response with CPR chest compressions and use of an AED can increase the odds of survival.

An AED sends an electric shock to the heart to try to restore a normal rhythm.

11 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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Additional Reading

By Rod Brouhard, EMT-P
Rod Brouhard is an emergency medical technician paramedic (EMT-P), journalist, educator, and advocate for emergency medical service providers and patients.