Sudden Cardiac Arrest (SCA)

Sudden Cardiac Arrest (SCA) occurs when the heart stops beating, abruptly and without warning


What is sudden cardiac arrest (SCA)?

Sudden cardiac arrest (SCA) occurs when an electrical issue causes your heart to stop beating and pumping blood suddenly. The lack of blood flow to the brain and other organs can cause a person to lose consciousness, become disabled, or die if not treated immediately.

It is essential to understand that SCA is not the same as a heart attack. A heart attack occurs when blood flow to the heart is blocked, whereas sudden cardiac arrest occurs when the heart malfunctions and suddenly stops beating. Think of a heart attack as a "circulation" or "plumbing" problem and SCA as an "electrical" problem.


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Sudden Cardiac Arrest

SCA Statistics (as of 2022*)
  • SCA affects 1,000 Americans of all ages each day.
  • More than 65% of Americans not only underestimate the seriousness of SCA but also incorrectly believe SCA is a type of heart attack.
  • There are more than 356,000 out-of-hospital cardiac arrests (OHCA) annually in the U.S., nearly 90% of them fatal.
  • In 2020, the location of OHCA in adults was most often a home or residence (73.9%), followed by public settings (15.1%) and nursing homes (10.9%). 
  • OHCA was witnessed by a layperson in 37.1% of cases or by a 911 responder in 12.8% of cases. For 50.1% of cases, collapse was not witnessed.

*Source: Sudden Cardiac Arrest Foundation

What causes SCA?

The most common cause of SCA is a dangerous and abnormal heart rhythm called ventricular fibrillation (VF). In VF, the electrical signals that control the lower chambers of the heart (ventricles) become disorganized or chaotic. This malfunction sends the ventricles into fibrillation, an extremely rapid and irregular quivering that cannot effectively pump blood to the body.

With no blood getting to the brain, a person experiencing VF loses consciousness within seconds. SCA and death can follow within minutes unless the heart is quickly shocked into its normal rhythm. To restore normal rhythm, a responder can use a defibrillator (a machine that delivers an electrical shock to the heart). The vast majority of VF victims die from SCA before they reach a hospital. However, prompt action by bystanders to alert first responders and begin CPR can improve the outcome.


Symptoms & Signs

SCA occurs abruptly and without warning; two-thirds of SCA deaths occur without prior indications of heart disease. SCA can happen to people of all ages and with all health conditions.

While signs and symptoms are often not present, there are certain risk factors for SCA, which include:

  • A prior heart attack: The majority of people who die of SCA show signs of a prior heart attack
  • A family history of heart failure, massive heart attack, or sudden death of an immediate family member before the age of 50
  • An abnormal heart rate or rhythm of unknown cause
  • An unusually rapid heart rate that comes and goes
  • Episodes of fainting of unknown cause
  • Some congenital heart defects before and after surgical repair
  • Low ejection fraction (EF): An ejection fraction measures how much blood is pumped by the ventricles with each heartbeat. A healthy heart pumps 55% or more of its blood with each beat; less than 35% indicates an elevated risk of SCA
  • Inherited heart rhythm disorders or heart muscle disorders like long QT syndrome  or hypertrophic cardiomyopathy


While there are often no signs or symptoms prior to SCA, there are things people can do to decrease the likelihood of experiencing it:

  • Live a healthy lifestyle:
    • Exercise regularly
    • Eat healthy foods
    • Maintain a healthy weight
    • Avoid smoking
  • Treat and monitor all health conditions including high blood pressure, high cholesterol, and diabetes. Ask your doctor about ejection fraction monitoring to determine if there is a risk.
  • Control or stop abnormal heart rhythms that may trigger life-threatening arrhythmias through proper medication, implantable cardioverter defibrillators (ICDs), and, in some cases, surgical procedures.
  • Know family heart history and understand the risks for other cardiovascular-related conditions, like heart failure. Communicate these to your physician. 


Minutes Matter

The time it takes for help and treatment to occur is a life-and-death situation during SCA. Ninety-five percent of those who experience SCA die because they do not receive life-saving defibrillation within four to six minutes before brain and permanent death begin to occur. CPR can provide circulation until a normal rhythm can be restored.

Follow these steps if an SCA emergency is suspected:

  1. Know the signs of SCA and react quickly. SCA strikes immediately and without warning. Victims will fall to the ground/collapse, become unresponsive, and will not breathe normally or at all.
  2. Call 911 as soon as possible.
  3. Start CPR as quickly as possible. If you don't know CPR, conduct Hands-Only CPR, which provides chest compressions by pushing hard and fast in the middle of the victim's chest with minimal interruptions at approximately 100 beats per minute (or hum the Bee Gees song "Staying Alive"). Studies of real emergencies have shown Hands-only CPR to be equally or more effective than conventional CPR.
  4. If available, use an automated external defibrillator (AED) immediately. AEDs are computerized medical devices that can check a person's heart rhythm and recognize and deliver a shock to a heart that needs it. AEDs are increasingly available in public locations, such as airports, gyms, malls, and office buildings. These devices will only deliver a shock when a life-threatening heart rhythm is detected.



Call-Push-Shock (CPS) is a national collaborative movement co-sponsored by Parent Heart Watch (PHW) and the Sudden Cardiac Arrest Foundation (SCAF) and endorsed by the Heart Rhythm Society. It is designed to drive public awareness, understanding, and action in cases of out-of-hospital cardiac arrest and increase survival rates by speaking in one voice across multiple organizations. 

You can triple a victim’s chance of survival when you take these immediate lifesaving actions:

  1. Call 911 and follow the emergency dispatcher’s instructions.
  2. Start CPR. Push hard and fast in the center of the chest; 100 to 120 compressions per minute.
  3. Use an AED if available. Follow step-by-step audio/visual instructions and remember that an AED cannot hurt the person, it can only help.



Create a Plan

Emergency Action Plan

As previously mentioned, statistics indicate that about 50% of cardiac arrest events are witnessed. Because many of these events may occur in public places or during community gatherings (e.g., schools, sporting events, concerts, etc.), having a prepared plan of action in the case of a sudden cardiac arrest has gained widespread recognition.

These “emergency action plans” can be found in local area high schools, professional sporting events, and health clubs in many states. The plans include identification and access to AEDs, CPR training for staff and teachers at schools, having CPR-trained staff or medical personnel at sporting events, and promoting CPR training for lay providers.

You can help save lives by ensuring emergency action plans and AEDs are present and accessible in your community and/or schools. 

Terms & Resources


October is SCA Awareness Month

Because SCA is a public health crisis striking 1,000 people a day in the U.S. alone, October was designated SCA Awareness Month. Every October, patient advocacy organizations and healthcare providers raise awareness about SCA and the critical importance of bystander intervention with CPR and automated external defibrillators (AEDs). Survival from SCA depends on the quick actions of people nearby who call 911, start CPR, and use an AED to restart the heart.


Additional SCA Resources*

*These links are provided as a convenience and for informational purposes only; they do not constitute an endorsement or approval by the Heart Rhythm Society.

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