Learn more about Sudden Cardiac Arrest through our Frequently Asked Questions below.

Sudden Cardiac Arrest (SCA) is a life-threatening emergency that occurs when the heart suddenly stops beating. It strikes people of all ages who may seem to be healthy, even children and teens. When SCA happens, the person collapses and doesn’t respond or breathe normally. They may gasp or shake as if having a seizure. SCA leads to death in minutes if the person does not get help right away. Survival depends on people nearby calling 911, starting CPR¹, and using an AED² (if available) as soon as possible.

¹CPR: Cardiopulmonary resuscitation is when you push hard and fast on the center of chest to make the heart pump. Compressions may be given with or without rescue breaths.

²AED: Automated external defibrillator is a device that analyzes the heart and if it detects a problem may deliver a shock to restart the heart’s normal rhythm.

SCA can result from cardiac causes (abnormalities of the heart muscle or the heart’s electrical system), external causes (drowning, trauma, asphyxia, electrocution, drug overdose, blows to the chest), and other medical causes such as inflammation of the heart muscle due to infection. Most SCAs are caused by an abnormal heart rhythm (arrhythmia). The most common life-threatening arrhythmia is ventricular fibrillation, which is an erratic, disorganized firing of impulses from the ventricles (the heart’s lower chambers). When this occurs, the heart is unable to pump blood and death will occur within minutes if left untreated. Heart attacks can also lead to SCA.

Usually, the first sign of SCA is loss of consciousness (fainting). Typically, the person collapses and doesn’t respond or breathe normally. They may gasp or shake as if having a seizure.

SCA is the third leading cause of death in the U.S. It affects about 1,000 people outside hospital settings every day. Unfortunately, only one in 10 victims survive.

No. While the average SCA victim is about 60-years-old, SCA affects people of all ages—even children and teens. Thousands of youth under the age of 18 experience SCA each year in the U.S.

No. SCA is an electrical problem in the heart. When people have SCA, they are not awake, their hearts are not beating, and they are unable to communicate. Symptoms of SCA include sudden loss of responsiveness and absence of normal breathing. In contrast, a heart attack is a circulatory problem in the heart. When people have heart attacks, they are awake, their hearts are beating, and they are able to communicate. Symptoms of heart attack can include chest discomfort; pain or discomfort in one or both arms, the back, neck, jaw or stomach; shortness of breath; sweating; nausea; and lightheadedness. Heart attacks can lead to SCA, but there also are many other causes.

When SCA happens outside a hospital setting, it occurs most often in a home or residence, followed by public settings and nursing homes. About 7 in 10 events occur in home settings.

Risk factors for SCA include:

  • Low ejection fraction or weak heart muscle
  • Prior heart attack
  • Heart failure
  • Abnormal heart rate or heart rhythm (arrhythmia)
  • Family history of arrhythmia
  • Family history of sudden cardiac death
  • Congenital heart defects
  • Hypertrophic cardiomyopathy (a thickened heart muscle that especially affects the ventricles)
  • Viral infection in the heart
  • History of syncope (fainting)
  • Coronary artery disease (CAD) and risk factors for CAD, including smoking, high blood pressure, diabetes, high cholesterol, obesity, and a sedentary lifestyle
  • Significant changes in blood levels of potassium and magnesium (e.g., from using diuretics)
  • Recreational drug use.

Ejection fraction (EF) refers to how well the heart is pumping. It's the percentage of blood that is pumped out of the heart’s main pumping chamber during each heartbeat. If the EF is low (35% or lower), the person is at increased risk for sudden cardiac death. It is important to know that the EF can change over time.

No. SCA often is the first indication of a heart problem.

While there are a number of possible causes, there are three common causes. One cause is Hypertrophic Cardiomyopathy (HCM), a congenital heart muscle disease in which the walls of the heart’s left ventricle become abnormally thickened. The structural abnormality can lead to obstruction of blood flow from the heart, causing loss of consciousness and an irregular heartbeat, leading to SCA. Another cause, Long QT syndrome, is an often-unrecognized congenital condition that predisposes the child to an abnormality in the heart’s electrical system that can lead to SCA. Episodes are most commonly triggered by physical exertion or emotional stress. Finally, commotio cordis is an electrical disturbance caused by a blow to the chest. It occurs most often in baseball, but has been reported in other sports and situations in which there is a blow to the chest.

Living a healthy lifestyle—exercising regularly, eating healthy foods, maintaining a healthy weight, and avoiding smoking—can help prevent SCA. Monitoring and controlling blood pressure, cholesterol levels and diabetes is also important. If there is a family history of SCA, it is important to be checked by a cardiologist or electrocardiologist. If abnormal heart rhythms (arrhythmias) are detected, they can be treated through implantable cardioverter defibrillator (ICD) therapy, use of medications such as ACE inhibitors, beta blockers and calcium channel blockers, and catheter ablation. Some patients, especially those who have had previous heart attacks, may benefit from the use of wearable cardioverter defibrillators (WCDs).

An implantable cardioverter-defibrillator (ICD) is a battery-powered device placed under the skin to monitor the heart rate. If an abnormal heart rhythm is detected (i.e., the heart is beating chaotically or too fast), the device will deliver a shock to restore a normal heartbeat. ICDs can prevent cardiac arrest in high-risk patients.

A wearable cardioverter defibrillator (WCD) is prescribed for patients at risk of SCA. It consists of a garment, an electrode belt, and a monitor. While some defibrillator devices are implanted under the skin, the wearable defibrillator is worn under the clothes, directly against the patient’s skin.

SCA is treatable most of the time—especially when it is due to an electrical abnormality called ventricular fibrillation—as long as it is treated quickly. Treatment includes cardiopulmonary resuscitation (CPR) and use of defibrillators. This treatment must be provided immediately to be effective, ideally within three to five minutes after collapse. Even the fastest emergency medical services may not be able to reach a victim this quickly. That is why prompt action by bystanders is critical and why it is so important that more laypersons learn CPR and how to use an automated external defibrillator (AED).

Laypersons should be prepared to recognize the emergency, call 911, give CPR and use the nearest AED. If the person is not responsive and not breathing normally, one should suspect SCA and start CPR. This has been called the "No-No-Go" protocol. When a person suffers cardiac arrest, he or she is clinically dead, but life can often be restored with immediate bystander action.

Subsequent care includes administration of medications and other advanced cardiac life support techniques by emergency medical personnel. Patients who have been successfully resuscitated but remain in a coma after cardiac arrest due to ventricular fibrillation (VF) may benefit from mild therapeutic hypothermia (cooling), which can improve the chances of survival with good brain function. SCA survivors should see heart specialists (cardiologists and electrophysiologists) for follow-up care.

CPR, or cardiopulmonary resuscitation, involves pushing on the center of the chest (between the nipples) hard and fast (100-120 pumps per minute) to circulate oxygenated blood already in the body to the brain and other organs.

An AED, or automated external defibrillator, is a device that automatically analyzes heart rhythms and advises the operator to deliver a shock if the heart is in a fatal heart rhythm. It is designed for use by untrained bystanders. AEDs are safe and cannot hurt the victim.

Yes. The chances of survival from SCA increase dramatically if the victim receives immediate CPR and treatment with an automated external defibrillator (AED). AEDs are designed for use by laypersons and provide visual and voice prompts. They will not shock the heart unless shocks are needed to restore a healthy heartbeat. Bystander intervention with CPR and AEDs can greatly improve the likelihood of survival. In fact, if bystanders use AEDs before EMS arrival, survival rates can be as high as 50%.

A computer inside the AED analyzes the victim’s heart rhythm. The device determines whether a shock is needed. Some devices shock the victim automatically if a shock is needed. Other devices require that the operator press a button to deliver the shock. The shock is delivered through pads applied to the victim’s bare chest. The shock stuns the heart, stopping abnormal heart activity and allowing a normal heart rhythm to resume.

An AED is designed for use by any bystander, regardless of training. The AED uses voice and visual prompts to advise the user how to apply electrode pads and whether or not to administer a shock. Some devices shock automatically if the victim has a fatal heart rhythm. Training is recommended since many victims also need CPR (cardiopulmonary resuscitation).

No. Most SCA victims will die if they are not treated immediately. Your actions can only help. AEDs are designed in such a way that they will only shock victims who need to be shocked.

No, not if you use it properly. The electric shock is programmed to go from one pad to the other through the victim's chest. Basic precautions, such as not touching the victim during the shock, ensure the safety of rescuers and bystanders.

Yes. AEDs can be used safely as long as the electrode pads do not come into contact with the metal surface.

If the victim is wearing a bra, remove it before placing electrode pads.

Never place AED electrode pads directly on top of medication patches. If the patch is in the way of the AED pads, remove it and wipe off the area with the victim's shirt. Do not touch the patch with bare skin. Then apply the pads to the clean, bare skin.

If the victim has an implantable pacemaker or defibrillator with a battery pack (visible as a lump under the skin), avoid placing the pad directly on top of the implanted medical device.

AEDs are designed to treat victims in SCA with an irregular heart rhythm called ventricular fibrillation (VF). AEDs work best in these victims if they are used quickly and if the victim has received cardiopulmonary resuscitation (CPR).

Defibrillators sometimes used on ambulances and in hospitals, and often seen on TV, are manual defibrillators. They are larger than AEDs and are designed to be used by medical personnel with special training. In contrast, AEDs are smaller, computerized devices designed so that virtually any operator can use them by simply following the audio and visual prompts.

Logical locations for AED placement include police cars, airports, train, bus and subway stations, highway rest stops, sports arenas, doctor and dentist offices, health clinics, fitness clubs, shopping malls, large grocery stores, theatres, workplaces, schools, churches and retirement communities. Research has shown some of the best locations for AED placement are in 24-hour coffee shops or near ATMs. Increasingly, consumers are choosing to purchase AEDs for their homes and vehicles, since most SCAs outside hospital settings occur in home settings.

A prescription from a physician is required for purchasing some AED models. However, at least one model has been cleared by the Food and Drug Administration for use without a prescription and is available over the counter.

No. CPR is critical until the AED arrives at the scene. High-quality CPR can greatly improve the chances of survival.

People who are at risk for SCA may want to consider having an AED at home. Regardless of known risk, since seven out of 10 SCAs occur at home, placing these devices in homes could save many lives.

No. A person who has suffered Sudden Cardiac Arrest is clinically dead. It is not possible to cause further injury by performing CPR or using an AED. The federal Cardiac Arrest Survival Act and state Good Samaritan laws are designed to protect laypersons from legal liability risk. Although laws vary from state to state, they generally encourage bystanders and the lay public to perform CPR and to use an AED. Depending on state law, the categories of people who are given protection include the lay public and sometimes first responders and medical professionals. Depending on state law, protection is granted unless the responder is negligent (fails to provide reasonable care), or grossly negligent (acts with a conscious disregard for the safety of the victim).

About one in 10 EMS-treated SCA victims survives. However, there are large regional variations in survival to hospital discharge, which are largely due to bystander intervention with CPR and AEDs. When bystanders give CPR, survival rates can triple. When bystanders give CPR and use AEDs, survival rates can be as high as 50%.

Therapeutic hypothermia (TH) is considered an important therapy for a comatose survivor of cardiac arrest—a patient whose heart stopped beating, was restarted during cardiopulmonary resuscitation (CPR), and who remains minimally responsive immediately after the event. It is endorsed by the American Heart Association and is performed by lowering the body temperature to 32-34ºC (approximately 90 to 93ºF). Normal body temperature is 98.6º F or 37ºC. TH works by protecting the brain and other vital organs. It lowers oxygen requirements, decreases swelling, and limits the release of toxins, which can cause cells to die. TH has been shown to improve neurological outcomes and increase survival in patients who remain in a coma after successful CPR.

Most people who survive SCA can return to their previous level of functioning. All survivors need follow-up care with physicians who specialize in heart conditions (cardiologists and electrophysiologists).

Some survivors of cardiac arrest experience medical problems, including impaired consciousness and cognitive deficits. Functional recovery continues over the first six to 12 months after out-of-hospital cardiac arrest in adults. It is common for survivors to have memory loss and to experience depression and anxiety for some time after their event.