Health Topic

Sudden Cardiac Arrest

In sudden cardiac arrest (SCA), an irregular heart rhythm causes the heart to stop beating. Without quick treatment, it causes sudden cardiac death. Learn more.

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Also called: Cardiac arrest · SCA

Important: This page is general information, not medical advice. It does not recommend or prescribe any treatment. Always consult your doctor or pharmacist before starting, stopping or changing any medicine.

About Sudden Cardiac Arrest

Sudden cardiac arrest (SCA) is a condition in which the heart suddenly stops beating. When that happens, blood stops flowing to the brain and other vital organs. If it is not treated, SCA usually causes death within minutes. But quick treatment with a defibrillator may be lifesaving.

A heart attack is different from an SCA. A heart attack happens when blood flow to the heart is blocked. During a heart attack, the heart usually doesn't suddenly stop beating. With an SCA, the heart stops beating.

Sometimes an SCA can happen after or during recovery from a heart attack.

Your heart has an electrical system that controls the rate and rhythm of your heartbeat. An SCA can happen when the heart's electrical system is not working right and causes irregular heartbeats. Irregular heartbeats are called arrhythmias. There are different types. They may cause the heart to beat too fast, too slow, or with an irregular rhythm. Some can cause the heart to stop pumping blood to the body; this is the type that causes SCA.

Certain diseases and conditions can cause the electrical problems that lead to SCA. They include:

  • Ventricular fibrillation, a type of arrhythmia where the ventricles (the heart's lower chambers) don't beat normally. Instead, they beat very fast and very irregularly. They can't pump blood to the body. This causes most SCAs.
  • Coronary artery disease (CAD), also called ischemic heart disease. CAD happens when the arteries of the heart cannot deliver enough oxygen-rich blood to the heart. It is often caused by the buildup of plaque, a waxy substance, inside the lining of larger coronary arteries. The plaque blocks some or all of the blood flow to the heart.
  • Some types of physical stress can cause your heart's electrical system to fail, such as Intense physical activity in which your body releases the hormone adrenaline. This hormone can trigger SCA in people who have heart problems.
  • Very low blood levels of potassium or magnesium. These minerals play an important role in your heart's electrical system.
  • Major blood loss
  • Severe lack of oxygen

You are at higher risk for SCA if you:

  • Have coronary artery disease (CAD). Most people with SCA have CAD. But CAD usually doesn't cause symptoms, so they may not know that they have it.
  • Are older; your risk increases with age
  • Are a man; it is more common in men than women
  • Are Black or African American, especially if you have other conditions such as diabetes, high blood pressure, heart failure, or chronic kidney disease
  • Have a personal history of heartbeats that aren't regular (arrhythmia)
  • Have a personal or family history of SCA or inherited disorders that can cause arrhythmia
  • Have a problem with drug or alcohol use
  • Have had a heart attack
  • Have heart failure

Usually, the first sign of SCA is loss of consciousness (fainting). This happens when the heart stops beating.

Some people may have a racing heartbeat or feel dizzy or light-headed just before they faint. And sometimes people have chest pain, shortness of breath, nausea, or vomiting in the hour before they have an SCA.

SCA happens without warning and requires emergency treatment. Health care providers rarely diagnose SCA with medical tests as it's happening. Instead, it is usually diagnosed after it happens. Providers do this by ruling out other causes of a person's sudden collapse.

If you are at high risk for SCA, your provider may refer you to a cardiologist, a doctor who specializes in heart diseases. The cardiologist may ask you to get various heart health tests to see how well you heart is working. He or she will work with you to decide whether you need treatment to prevent SCA.

SCA is an emergency. A person having SCA needs to be treated with a defibrillator right away. A defibrillator is a device sends an electric shock to the heart. The electric shock can restore a normal rhythm to a heart that's stopped beating. To work well, it needs to be done within minutes of the SCA.

Most police officers, emergency medical technicians, and other first responders are trained and equipped to use a defibrillator. Call 9-1-1 right away if someone has signs or symptoms of SCA. The sooner you call for help, the sooner lifesaving treatment can begin.

Many public places such as schools, businesses, and airports have automated external defibrillators (AEDs). AEDs are special defibrillators that untrained people can use if they think that someone has had SCA. AEDS are programmed to give an electric shock if they detect a dangerous arrhythmia. This prevents giving a shock to someone who may have fainted but isn't having SCA.

If you see someone who you think has had SCA, you should give cardiopulmonary resuscitation (CPR) until defibrillation can be done.

People who are at risk for SCA may want to consider having an AED at home. Ask your cardiologist to help you decide whether having an AED in your home might help you.

If you survive SCA, you'll likely be admitted to a hospital for ongoing care and treatment. In the hospital, your medical team will closely watch your heart. They may give you medicines to try to reduce the risk of another SCA.

They will also try to find out what caused your SCA. If you're diagnosed with coronary artery disease, you may have an angioplasty or coronary artery bypass surgery. These procedures help restore blood flow through narrowed or blocked coronary arteries.

Often, people who have had SCA get a device called an implantable cardioverter defibrillator (ICD). This small device is surgically placed under the skin in your chest or abdomen. An ICD uses electric pulses or shocks to help control dangerous arrhythmias.

You may be able to lower your risk of SCA by following a heart-healthy lifestyle. If you have coronary artery disease or another heart disease, treating that disease can also lower your risk of SCA. If you have had an SCA, getting an implantable cardioverter defibrillator (ICD) can lower your chance of having another SCA.

It sits within Blood, Heart and Circulation.

The lead U.S. institute for this subject is the National Heart, Lung, and Blood Institute.

When to speak to someone. Reading about a topic cannot tell you whether it applies to you. Speak to a doctor or pharmacist if symptoms are severe, sudden, getting worse, or simply not going away — and seek emergency care immediately for chest pain, breathing difficulty, sudden weakness or confusion, or a serious allergic reaction.

Research on Sudden Cardiac Arrest

380 studies areregistered for this condition on ClinicalTrials.gov, the U.S. National Library of Medicine's public registry. A selection is below — the links go straight to the registry entry, not to a summary of ours.

What a registered study does and does not mean. Registration means a study exists and has been declared publicly. It says nothing about whether the treatment being tested works, is safe, or is available to you. Many studies find no benefit — that is what research is for. Never seek out an experimental treatment on the strength of a registry entry alone.

Research currently under way

Research already completed

Study data from ClinicalTrials.gov, a service of the U.S. National Library of Medicine. Retrieved 2026-07-30. Registry entries are supplied by study sponsors and investigators; ClinicalTrials.gov does not verify their scientific validity. PocketsInfo is not affiliated with, and not endorsed by, the NLM or the NIH.

Where to read more

Rather than paraphrase, we point you to the primary sources. Every link below is to a government health agency, a national institute or a recognised medical body — grouped by what you are trying to find out.

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Treatments and Therapies

Prevention and Risk Factors

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Clinical Trials

Medical subject headings

Clinicians and researchers index this subject under Heart Arrest. These are the terms to use when searching medical literature.

This page is built from the MedlinePlus health topic record for Sudden Cardiac Arrest, a service of the U.S. National Library of Medicine (NLM), National Institutes of Health. Information is from MedlinePlus.gov. PocketsInfo is not affiliated with, and is not endorsed by, the NLM or the NIH. Retrieved 30 July 2026.