Defibrillators are devices that restore a normal heartbeat by sending an electric pulse or shock to the heart. They are used to prevent or correct an arrhythmia, a heartbeat that is uneven or that is too slow or too fast. Defibrillators can also restore the heart’s beating if the heart suddenly stops.

Different types of defibrillators work in different ways. Automated external defibrillators (AEDs), which are in many public spaces, were developed to save the lives of people experiencing sudden cardiac arrest. Even untrained bystanders can use these devices in an emergency.

Other defibrillators can prevent sudden death among people who have a high risk of a life-threatening arrhythmia. They include implantable cardioverter defibrillators (ICDs), which are surgically placed inside your body, and wearable cardioverter defibrillators (WCDs), which rest on the body. It can take time and effort to get used to living with a defibrillator, and it is important to be aware of possible risks and complications.

An arrhythmia is any disorder of your heart rate or rhythm. It means that your heart beats too quickly, too slowly, or with an irregular pattern. Most arrhythmias result from problems in the electrical system of the heart. If your arrhythmia is serious, you may need a cardiac pacemaker or an implantable cardioverter defibrillator (ICD). They are devices that are implanted in your chest or abdomen.

A pacemaker helps control abnormal heart rhythms. It uses electrical pulses to prompt the heart to beat at a normal rate. It can speed up a slow heart rhythm, control a fast heart rhythm, and coordinate the chambers of the heart.

An ICD monitors heart rhythms. If it senses dangerous rhythms, it delivers shocks. This treatment is called defibrillation. An ICD can help control life-threatening arrhythmias, especially those that can cause sudden cardiac arrest (SCA). Most new ICDs can act as both a pacemaker and a defibrillator. Many ICDs also record the heart's electrical patterns when there is an abnormal heartbeat. This can help the doctor plan future treatment.

Getting a pacemaker or ICD requires minor surgery. You usually need to stay in the hospital for a day or two, so your doctor can make sure that the device is working well. You will probably be back to your normal activities within a few days.

Defibrillators can be used in children, teens, and adults. AEDs are used to treat sudden cardiac arrest. Your doctor may recommend an ICD or WCD to treat an arrhythmia and prevent new or repeat sudden cardiac arrests.

Who needs an AED?

AEDs can save the life of someone having sudden cardiac arrest, when the heart suddenly and unexpectedly stops beating.

AEDs can be used for adults, as well as for children as young as 1 year old. Some devices have pads and cables designed especially for children.

Doing cardiopulmonary resuscitation, or CPR, on someone having sudden cardiac arrest also can improve his or her chance of survival.

Who needs an ICD?

ICDs can correct a dangerous arrhythmia or keep an irregular heartbeat from triggering sudden cardiac arrest. Life-threatening arrhythmias can develop for many reasons and can affect people of any age, from newborns to older adults. Your doctor may recommend an ICD if you have a type of arrhythmia that causes your heart’s ventricles to quiver instead of pumping blood. This type of arrhythmia is most likely to cause sudden cardiac arrest.

If you have the following conditions, you may be at risk for a life-threatening arrhythmia and your doctor may recommend an ICD:

• You survived sudden cardiac arrest.
• You developed an arrhythmia during or after treatment for a heart attack.
• You have a genetic condition that causes arrhythmia. This includes having congenital heart disease or an inherited conduction disorder.
• You have a neuromuscular disorder. For example, the progression of muscular dystrophy can damage the heart and cause unpredictable heart rhythms. This can lead to unexplained fainting and a high risk of death.
• You have an abnormally slow heart rate or other problem with the heart’s electrical signals.
• You have cardiac sarcoidosis.
• You have poor heart function following a procedure to improve blood flow.
• Your doctor detected an arrhythmia during an electrocardiogram (EKG) or stress test. If this happened several times, you may be at increased risk.

Who needs a WCD?

WCDs are used to protect against sudden cardiac arrest in certain circumstances, such as if you are at risk of arrhythmia for just a short time. This might occur under these conditions:

• You are recovering from a heart attack.
• You are waiting for a heart transplant.
• You are fighting an infection.
• You are removing or waiting to replace your ICD.

There are three types of defibrillators: AEDs, ICDs, and WCDs. Each type works by checking for arrhythmias, or irregular heart rhythms. Once detected, each defibrillator will send a shock to restore a normal rhythm. Learn more about how the three types of defibrillators work.

How do AEDs work?

An AED is a lightweight, battery-operated, portable device that checks the heart’s rhythm and sends a shock to the heart to restore a normal rhythm. The device is used to help people having sudden cardiac arrest.

Sticky pads with sensors, called electrodes, are attached to the chest of someone who is having cardiac arrest. The electrodes send information about the person's heart rhythm to a computer in the AED. The computer analyzes the heart rhythm to find out whether an electric shock is needed. If needed, the electrodes deliver the shock.

How do ICDs work?

ICDs are placed surgically in the chest or abdomen, where it checks for arrhythmias. Arrhythmias can interrupt the flow of blood from your heart to the rest of your body or cause your heart to stop. The ICD sends a shock to correct the arrhythmia.

An ICD can give off a low-energy shock to speed up or slow down an abnormal heart rate or a high-energy shock, which can correct a fast or irregular heartbeat. If the low-energy shocks do not restore your normal heart rhythm, the device will switch to high-energy shocks for defibrillation. The device also will switch to high-energy shocks if your ventricles start to quiver rather than contract strongly. ICDs are similar to pacemakers, but pacemakers deliver only low-energy electrical shocks.

ICDs have a generator connected to wires to detect your heart’s pulses and deliver a shock when needed. Some models have wires that rest in one or two chambers of the heart. Others do not have wires threaded into the heart chambers but rest on the heart to monitor its rhythm.

The ICD can also record the heart's electrical activity and heart rhythms. The recordings can help your doctor fine-tune the programming of your device so it works better to correct irregular heartbeats. Your device will be programmed to respond to the type of arrhythmia you are most likely to have.

How do WCDs work?

WCDs have sensors that attach to the skin. They are connected by wires to a unit that checks your heart’s rhythm and delivers shocks when needed. Like an ICD, the WCD can deliver low- and high-energy shocks. The device has a belt attached to a vest and is worn under your clothes. Your doctor will fit the device to your size. The device is programmed to detect a particular heart rhythm.

The sensors detect when an arrhythmia occurs and notifies you with an alert. You can turn off the alert to prevent a shock if not needed, but if you do not respond, the device will administer a shock to correct the rhythm. Typically, this happens within one minute. The device can deliver repeated shocks during an episode. After each episode, the sensors must be replaced.

The device can also send a record of your heart’s activity to your doctors.

AEDs are found in many public spaces. They may be used in an emergency to help someone who is experiencing sudden cardiac arrest. Learn how to recognize sudden cardiac arrest emergencies—when you might use an AED, how to find an AED if you need one, and how to use an AED until help arrives.

When to use an AED

A person whose heart stops from sudden cardiac arrest must get help within 10 minutes to survive. Fainting is usually the first sign of sudden cardiac arrest. If you think someone may be in cardiac arrest, try the following steps:

• If you see a person faint or if you find a person already unconscious, first confirm that the person cannot respond. The person may not move, or his or her movements may look like a seizure.
• You can shout at or gently shake the person to make sure he or she is not sleeping, but never shake an infant or young child. Instead, you can gently pinch the child to try to wake him or her up.
• Check the person’s breathing and pulse. If the person is not breathing and has no pulse or has an irregular heartbeat, prepare to use the AED as soon as possible.

Where to find an AED

You often find AEDs in places with large numbers of people, such as shopping malls, golf courses, gyms and swimming pools, businesses, airports, hotels, sports venues, and schools. You can also purchase a home-use AED.

The AED is in a case about the size of a large first-aid kit. Many AEDs have a heart logo in red or green. Large letters on the case or the wall where it is stored might spell out A–E–D.

How to use an AED

Even someone without special training can respond in an emergency by following the instructions relayed by the device. If someone is having sudden cardiac arrest, using an AED and giving CPR can save that person’s life. When using an AED:

• Call 9-1-1 or have someone else call 9-1-1. If two rescuers are present, one can provide CPR while the other calls 9-1-1 and gets the AED.
• Make sure the area around the person is clear; touching the person could interfere with the AED’s reading of the person’s heart.
• If an electric pulse or shock is needed to restore a normal rhythm, the AED uses voice prompts to tell you when and how to give the shock, and electrodes deliver it. Some AEDs can deliver more than one shock with increasing energy.
• The device may instruct you to start CPR again after delivering the shock.

Sudden cardiac arrest occurs when the heart suddenly and unexpectedly stops pumping blood. It can happen to anyone, at any time, and signs include sudden collapse and immediate loss of consciousness.

Unlike heart attacks, which are caused by a blockage in an artery to the heart, sudden cardiac arrest is caused when the heart’s electrical system malfunctions. This produces abnormal heart rhythms, called arrhythmias, that make the heart unable to pump blood.

If cardiac arrest does occur, rapid treatment with a medical device called an automated external defibrillator (AED) can be life-saving.

An AED is a type of computerized defibrillator that automatically analyzes the heart rhythm in people who are experiencing cardiac arrest. When appropriate, it delivers an electrical shock to the heart to restore its normal rhythm. The conversion of a ventricular arrhythmia to its normal rhythm by an electrical shock is called defibrillation.

Defibrillation is time-sensitive. The probability of survival decreases by 7 percent to 10 percent for every minute that a victim stays in a life-threatening arrhythmia.

The U.S. Food and Drug Administration (FDA) regulates AEDs as medical devices and evaluates them for safety and effectiveness before they are marketed.

Many AEDs Are in Plain Sight

You can find AEDs in many public places, including offices, schools, shopping malls, grocery stores, and airports.

Emergency first-responders are typically equipped with and trained to use AEDs. Some people with underlying cardiac conditions can be at a higher risk of sudden cardiac arrest. Your health care provider can tell you if a home AED is something you should consider.

How AEDs Work

An AED system includes an AED device and accessories, such as a battery, pad electrodes, and if applicable, an adapter. The devices give verbal instructions to users.

This is how they work:

• The user turns on the AED and follows the voice prompts. Some devices turn on automatically when the user opens the lid.
• The user attaches two sticky pads with sensors (called electrodes) on the chest of the person in cardiac arrest.
• The electrodes send information about the person’s heart rhythm to a processor in the AED, which then analyzes the rhythm to find out whether an electric shock is needed.
• If a defibrillation shock is needed, the AED uses the voice prompts to instruct when to press a button to deliver the shock. In some devices, the voice prompts announce that a shock is going to be delivered and the AED delivers the shock without intervention by the user.

Training to Use AEDs

AEDs are not difficult to use, but training in the use of AEDs is highly recommended. This training, in connection with CPR training, is offered by many major health organizations. Some training is available online.

Classes can teach you how to recognize the signs of a sudden cardiac arrest, when to call emergency medical services, how to do CPR, and how to use an AED.

Some people may be afraid to use an AED because they’re worried something may go wrong. But most states’ Good Samaritan laws and the Federal Cardiac Arrest Survival Act provide some protection for bystanders who respond to emergencies.

But as always, in an emergency, call 911 immediately. If you’re somewhere that has an emergency response system that includes a clearly visible number, call that number for assistance. In either case, an operator can give instructions on how you can help someone who has sudden cardiac arrest.

How the FDA Regulates AEDs

As part of its regulatory oversight, the FDA closely monitors reports of device malfunctions, and reviews reports from consumers and manufacturers of AEDs.

Although the FDA regulates AEDs as medical devices, it does not regulate the resuscitation guidelines for the use of these devices.

In February 2015, the FDA required manufacturers to have “premarket approval” before marketing AED devices and accessories necessary for the functionality of the AED, to better ensure quality design and manufacturing practices. Premarket approval is the most stringent type of device marketing review required by the FDA, and approval is based on a determination by the FDA, relying on valid scientific evidence, that there is a reasonable assurance that the device is safe and effective for its conditions of use.

The FDA maintains a list of AED devices that are FDA-approved. Certain AEDs that do not appear on the FDA-approved list are considered “legacy devices.” Although some of these legacy devices are still in use, they may no longer be legally marketed.

What this means for you:

If you own an AED, check the FDA’s list of approved AED devices to confirm the device is FDA-approved. Contact the AED manufacturer with any questions or concerns.

If a cardiac arrest emergency happens and an AED is available, know that AEDs can save lives, even legacy devices. The potential life-saving benefits of FDA-approved AEDs when used as intended outweigh the probable risks of using them, when accompanied by adequate directions and appropriate warnings. You should be confident in using these devices in life-threatening situations.

If your doctor recommends an ICD to treat an arrhythmia, your healthcare team will help you prepare for surgery. Learn about what to expect from the surgery and during the early days of your recovery. As with any surgery, there are risks involved.

Before and during surgery

You may have questions about your condition and whether an ICD is right for you. Discuss them with your doctor. You may be able to choose between different ICD models with different benefits and risks. Your doctor will help you make the decision that is right for you.

Placing an ICD requires minor surgery, which usually is done in a hospital. Your doctor will discuss the procedure with you. This is a good time to ask questions.

Before the surgery, members of your healthcare team will give you medicines to relax you and to numb the area where the device will go. They may also give you antibiotics to prevent infections.

Typically, the ICD is placed under your breastbone or along your ribs. In infants, it can be placed in the abdomen. With some devices, your doctor may first thread one or two sensor wires through your blood vessels into the chambers of your heart. With others, a single sensor wire is placed along the breastbone. The doctors will use a monitor to guide the wires and put them in the right place.

Once the device is in place, your doctor will test it. Then your doctor will sew up the cut. The entire surgery takes a few hours.

Recovery from surgery

You may be able to leave the hospital once the medicines you received for the surgery wear off. You can then continue your recovery at home.

Follow the instructions you receive. Your healthcare team may tell you to take these steps:

• Check the cut on your chest often and keep the area clean and dry.
• Call your doctor if any swelling or bleeding occurs or if you develop a fever.
• Take over-the-counter pain medicines such as acetaminophen if you feel pain. But talk to your doctor first; he or she may tell you to avoid taking ibuprofen or other kinds of pain medicines, for example.
• Ask your doctor when you can resume taking medicines that you took before the surgery, how soon you can take a shower, and when you can return to work. You will probably have to avoid driving for at least a week while you recover from your surgery. Your doctor may also ask you to avoid high-impact activities and heavy lifting for about a month.

At your next scheduled appointment, ask your doctor about living with an ICD and what to do when you feel an electric pulse or shock from your device.

Possible surgery-related complications

As with any surgery, there are some risks related to the surgery used to place an ICD. Although they are rare, possible complications include:

• A bad reaction to the medicine used to make you relax or sleep during the surgery
• A collapsed lung
• A defibrillator wire puncturing the heart or a vessel
• Bleeding from the site where the device was placed
• Blood vessel, heart, or nerve damage
• Swelling, bruising, or infection at the area where the device was placed
• Venous thromboembolism

Some ICD models have a lower risk of clots, puncture, and infection.

After sudden cardiac arrest, surgery to implant an ICD, or a fitting for a WCD, you will need regular visits with your doctor to check your condition, the device, or any medicines you are taking. You can get an ID card with information about your device to keep with you. It can be helpful in an emergency, to show airport security, or for medical personnel who need to know more about your device. If you have an ICD, be aware of the signs of complications with your device.

What to expect from electric shocks

It takes time to get used to having an ICD or WCD. These devices can deliver electrical energy at different strengths to regulate your heart.

• Low-energy shocks. The low-energy electrical shocks your device gives are not painful. You may not notice them, or you may feel a fluttering in your chest.
• High-energy shocks. The high-energy shocks last only a fraction of a second, but they can be strong or painful. They may feel like thumping or a kick in the chest, depending on their strength. Before a shock, you may feel arrhythmia symptoms. If you feel one or two strong shocks over a short period and the symptoms go away, it may be a sign that the device is working. Notify your doctor’s office and set up an appointment that day or the next day. He or she will want to assess your condition and the device.
• Unnecessary shocks. During the adjustment period after your surgery, your device may deliver a shock when it is not needed. A damaged wire or a very fast heart rate due to extreme physical activity may trigger unnecessary shocks. These shocks can also occur if you forget to take your medicines. Some people also feel phantom shocks, even when the device does not detect an arrhythmia.

Make sure your WCD is fitted properly

You will be wearing it all the time, except when you are taking a shower or bath. Like shocks from ICDs, shocks from WCDs can be painful and sometimes cause burns. Your doctor will explain how to charge and change the batteries in your WCD.

Return to normal daily activities

Talk to your doctor about when you can return to normal activities, such as physical activity and driving.

• Physical activity. An ICD usually will not limit you from taking part in sports and exercise, including strenuous activities. You may need to avoid full-contact sports, such as football. Contact sports can damage your ICD or shake loose the wires in your heart. Ask your doctor how much and what types of physical activity are safe for you.
• Driving. You probably will be able to resume your typical driving patterns after you recover from surgery. However, if you received an ICD to prevent another sudden cardiac arrest or ventricular arrhythmia, it will probably be several months before your doctor says you are ready to drive again. This is because of the risks of fainting or getting a shock from your device. Your doctor may also suggest driving restrictions based on the activity recorded by your device.

Receive routine follow-up care

Once you have an ICD, you will visit your doctor at least every six months. At these visits, your doctor will examine the area where the device was implanted and check information about your heart rhythm that was recorded by the device. In between visits, your doctor can monitor data from your device remotely. If it is needed, he or she can adjust the device’s settings.

At the follow-up visits, your doctor may also take these steps:

• Prescribe or adjust your medicines to decrease the number of irregular heartbeats you have. Fewer irregular beats will mean fewer high-energy shocks that have to be sent to your heart.
• Check to make sure the device continues to work properly and that it has not shifted in your body or caused irritation or injury. Over time, your ICD may stop working well because its wires get dislodged or broken, its battery fails, your heart disease progresses, or other devices have disrupted its electrical signaling. Your doctor also may recommend an electrocardiogram (EKG) to check for changes in your heart’s electrical activity.
• Check to see whether you are at risk of heart failure. If device and medicine adjustments do not reduce your irregular heart rhythms, your doctor may suggest a procedure called ablation to stop excess electrical signals in your heart.
• Check to see whether the battery needs to be replaced. Batteries in ICDs last between five and seven years. When the batteries in your device run down, you will need surgery to replace them. Replacing the battery is less involved than the original surgery to implant the ICD. Ask your doctor whether the device generator or its wires need to be replaced, too.

Manage devices that can interfere with your ICD

Electrical devices and devices with strong magnetic fields can interfere with your ICD. You may not be able to sense when this happens. If something disrupts your ICD, step away from the disruptive device to help restore its normal working. To be safe, keep your ICD at least six inches away from the following devices, or, when necessary, use them only briefly:

• Cell phones. If you have an ICD on the left side of your chest, hold your cell phone to your right ear.
• Headphones. Most headphones have a magnetic element in them. Wear them as far away from your ICD as possible, and do not carry your headphones in a chest pocket.
• Metal detectors, such as those used for airport security. The risk of harm is low, but you can show your ID card and ask for alternative inspection.

Some medical procedures, including magnetic resonance imaging (MRI), can damage ICDs. This depends on the procedure and your device model. For example, some people with newer models can undergo MRI. Tell your dentist or doctor that you have an ICD and discuss your options with them. You can show them the card with information about your device.

Learn the warning signs of complications and make a plan

It is possible for a wire in an ICD to fire at the wrong time or become infected. Call your doctor if you have signs of symptoms that concern you, and if you have these signs in particular:

• Fainting
• Dizziness or feeling out of breath
• Fever
• Heart palpitations or chest pain

Go to a hospital emergency room if you feel many strong shocks from your device in a short time.

Occasionally an ICD does not work properly and cannot be fixed with changes in programming or medicine. If this happens, your doctor might have to replace the ICD. When you visit the doctor, ask whether the manufacturer has announced any problems with your device.

Tend to your emotional health

If you have survived sudden cardiac arrest, you may worry about whether it will happen again. After surgery to implant an ICD or fitting for a WCD, adjusting to the uncertainty of life with the device may cause fear, anxiety, and stress. When your device sends a strong shock, it may startle or distress you or cause you pain. This can make some people stop doing the things they used to do. After having sudden cardiac arrest or getting an ICD, some people report anxiety, depression, or other more serious emotional health concerns.

If you have survived cardiac arrest or are living with an ICD or WCD and experience anxiety or depression, tell your doctor about your concerns.

Heart disease, also called cardiovascular disease, can have serious consequences. It’s the leading cause of death for men and women in the United States. Medical devices approved by the U.S. Food and Drug Administration (FDA), such as pacemakers and defibrillators, have extended and improved the lives of millions of people living with heart disease.

The FDA evaluates certain devices for safety and effectiveness before they can be marketed to the public. These medical devices include certain devices used to treat cardiovascular disease, cardiovascular conditions, and other related issues. Many of these FDA-approved medical devices can be implanted in a person’s body, while others are used outside the body. Health care providers determine which cardiovascular devices, if any, are best for each patient.

Below are some categories of FDA-approved devices used to treat various cardiovascular issues. Types of heart devices include:

Automated external defibrillators (AEDs): Portable and automatic, these devices are often found in public places and can save lives. They can help restore normal heart rhythm in patients whose hearts suddenly and unexpectedly stop pumping blood, an event called cardiac arrest. AEDs analyze heart rhythm and can help rescuers determine whether a shock is needed to restore a normal heartbeat. These devices are not difficult to use, but training in the use of AEDs is highly recommended. Learn more about AEDs on the FDA’s website.

Cardiac ablation catheters: Long, thin flexible tubes that are threaded into or onto the heart, cardiac ablation catheters treat abnormally rapid heartbeats. They work by modifying small areas of heart tissue that are causing abnormal heart rhythms.

Cardiovascular angioplasty devices: These are long, thin, flexible tubes that are threaded into a heart or other blood vessel to open narrowed or blocked areas. They are intended to improve blood flow to the heart, reduce chest pain, and treat heart attacks.

Cardiac pacemakers: Small and battery-powered, pacemakers are implanted into the body. Used when the heart beats too slowly, they monitor the organ’s electrical impulses and, when needed, deliver electrical stimulation to make it beat at a more appropriate rate.

Implantable cardioverter defibrillators (ICDs): These devices monitor heart rhythms and deliver shocks if dangerously fast rhythms are detected. Many record the heart’s electrical patterns when certain abnormal rhythms occur, allowing doctors to review the patterns.

Prosthetic (artificial) heart valves: Used for replacing diseased or dysfunctional heart valves, which direct blood flow through the heart, these are available in two forms. Mechanical valves are made of man-made materials. The second type, called “bioprosthetic” valves, are made from tissue taken from animals or human cadavers.

Stents: Small, lattice-shaped, metal tubes that are inserted permanently into an artery, stents are intended to help improve blood flow. Some contain drugs that may reduce the chance that arteries will become blocked again.

Ventricular assist devices (VADs): Mechanical pumps that are intended to help weak hearts pump blood effectively, VADs were originally approved for short-term use until donor hearts became available. Some are now approved for long-term therapy in patients with severe heart failure who are not candidates for heart transplants.

When to Seek Medical Help

If you have questions or concerns about your heart, talk to your primary care doctor. If you feel like you’re having a heart attack or other emergency medical issues, immediately call 911.

Know the warning signs and symptoms of a heart attack. The chances of survival are greater when emergency treatment begins quickly.

Sudden cardiac arrest occurs when the heart suddenly and unexpectedly stops pumping blood. If cardiac arrest does occur, rapid treatment with an AED can be life-saving. Defibrillation is a time-sensitive issue. The probability of survival decreases by 7 percent to 10 percent for every minute that a victim stays in a life-threatening arrhythmia.

Emergency first-responders are typically equipped with and trained to use AEDs. AEDs are also often found in public areas, and people with CPR and AED training can use them to help a person in cardiac arrest.