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What Is Cardioversion?

Cardioversion (KAR-de-o-VER-shun) is a procedure that can restore a fast or irregular heartbeat to a normal rhythm. A fast or irregular heartbeat is called an arrhythmia (ah-RITH-me-ah).

Arrhythmias can prevent your heart from pumping enough blood to your body. They also can raise your risk for stroke, heart attack, and sudden cardiac arrest.


To understand arrhythmias, it helps to understand how the heart works. Your heart is a muscle; it has an internal electrical system that controls the rate and rhythm of your heartbeat. With each heartbeat, an electrical signal spreads from the top of your heart to the bottom.

As the signal travels, it causes your heart to contract and pump blood. The process repeats with each new heartbeat. (For more information about the heart's electrical system and a detailed animation, go to the Health Topics How the Heart Works article.)

A problem with any part of this process can cause an arrhythmia. During an arrhythmia, the heart can beat too fast, too slow, or with an irregular rhythm. Doctors use cardioversion to correct fast or irregular heartbeats.

Cardioversion is done two ways: using an electrical procedure or using medicines.

For the electrical procedure, your heart is given low-energy shocks to trigger a normal rhythm. You're temporarily put to sleep before the shocks are given. This type of cardioversion is done in a hospital as an outpatient procedure. "Outpatient" means you can go home after the procedure is done.

Using medicines to correct arrhythmias also is a form of cardioversion. This type of cardioversion usually is done in a hospital, but it also can be done at home or in a doctor's office.

This article only discusses the electrical cardioversion procedure.

Cardioversion isn't the same as defibrillation (de-fib-rih-LA-shun), although they both involve shocking the heart. Defibrillation gives high-energy shocks to the heart to treat very irregular and severe arrhythmias. It's used to restore normal heartbeats during life-threatening events, such as sudden cardiac arrest.


The success rate of cardioversion depends on the type of arrhythmia it’s used to treat. However, with all arrhythmias, the success rate is usually 75 percent or better.

Fast or irregular heartbeats can occur again after cardioversion. For this reason, you may need to have more than one cardioversion over time.

The procedure has some risks. For example, it may worsen arrhythmias. However, serious problems are rare.

Who Needs Cardioversion?

Your doctor may recommend cardioversion if you have an arrhythmia that's causing troublesome symptoms. These symptoms may include dizziness, shortness of breath, extreme fatigue (tiredness), and chest discomfort.

Atrial fibrillation (A-tre-al fih-brih-LA-shun), or AF, is a common type of arrhythmia treated with cardioversion. In AF, the heart's electrical signals travel through the heart's upper chambers (the atria) in a fast and disorganized way. This causes the atria to quiver instead of contract.

Atrial flutter, which is similar to AF, also might be treated with cardioversion. In atrial flutter, the heart's electrical signals travel through the atria in a fast, but regular rhythm.

Cardioversion sometimes is used to treat rapid heart rhythms in the lower heart chambers (the ventricles).

Cardioversion usually is a scheduled procedure. However, you may need an emergency cardioversion if your symptoms are severe.

For some people who have other heart conditions in addition to arrhythmias, cardioversion might not be the best treatment option. Talk with your doctor about whether cardioversion is an option for you.

What To Expect Before Cardioversion

You usually can't have any food or drinks for about 12 hours before having cardioversion (as your doctor advises).

You're at higher risk for dangerous blood clots during and after a cardioversion. The procedure can dislodge blood clots that have formed as the result of an arrhythmia.

Your doctor may prescribe anticlotting medicine to prevent dangerous clots. He or she may recommend that you take this medicine for several weeks before and after the cardioversion procedure.

To find out whether you need anticlotting medicine, you might have transesophageal echocardiography (TEE) before the cardioversion. TEE is a special type of ultrasound. An ultrasound is a test that uses sound waves to look at the organs and structures in the body.

TEE involves a flexible tube with a device at its tip that sends sound waves. Your doctor will guide the tube down your throat and into your esophagus (the passage leading from your mouth to your stomach). You’ll be given medicine to make you sleep during the procedure.

Your doctor will place the tube close to your heart, and the sound waves will create pictures of your heart. Your doctor will look at these pictures to see whether you have any blood clots.

The TEE will be done at the same time as the cardioversion or just before the procedure. If your doctor finds blood clots, he or she may delay your cardioversion for a few weeks. During this time, you'll take anticlotting medicine.

Even if no blood clots are found, your doctor may prescribe anticlotting medicine during and after the cardioversion to prevent dangerous blood clots from forming.

Before the cardioversion procedure, you’ll be given medicine to make you sleep. This medicine can affect your awareness when you wake up. So, you'll need to arrange for someone to drive you home after the procedure.

What To Expect During Cardioversion

A nurse or technician will stick soft pads called electrodes on your chest and possibly on your back. He or she may need to shave some areas on your skin to get the pads to stick.

The electrodes will be attached to a cardioversion machine. The machine will record your heart's electrical activity and send low-energy shocks through the pads to restore a normal heart rhythm.

Your nurse will use a needle to insert an intravenous (IV) line into a vein in your arm. Through this line, you’ll get medicine that will make you fall asleep.

While you're asleep, a cardiologist (heart specialist) will send one or more low-energy electrical shocks to your heart. You won't feel any pain from the shocks.

Your health care team will closely watch your heart rhythm and blood pressure during the procedure for any signs of complications.


The image shows a typical setup for a nonemergency cardioversion. Figure A shows an irregular heart rhythm recording (before the cardioversion). Figure B shows a normal heart rhythm recording (after the cardioversion). Figure C shows the patient lying in bed with cardioversion pads attached to his body. The doctor closely watches the procedure.

The image shows a typical setup for a nonemergency cardioversion. Figure A shows an irregular heart rhythm recording (before the cardioversion). Figure B shows a normal heart rhythm recording (after the cardioversion). Figure C shows the patient lying in bed with cardioversion pads attached to his body. The doctor closely watches the procedure.

Cardioversion takes just a few minutes. However, you'll likely be in the hospital for a few hours due to the prep time and monitoring after the procedure.

What To Expect After Cardioversion

Your health care team will closely watch you after the procedure for any signs of complications. Your doctor or nurse will let you know when you can go home. You’ll likely be able to go home the same day as the procedure.

You may feel drowsy for several hours after the cardioversion because of the medicine used to make you sleep. You shouldn't drive or operate heavy machinery the day of the procedure.

You'll need to arrange for someone to drive you home from the hospital. Until the medicine wears off, it also may affect your awareness and ability to make decisions.

You may have some redness or soreness on your chest where the electrodes were placed. This may last for a few days after the procedure. You also may have slight bruising or soreness at the site where the intravenous (IV) line was inserted.

Your doctor will likely prescribe anticlotting medicine for several weeks after the procedure to prevent blood clots. During this time, you also may take medicine to prevent repeat arrhythmias.

What Are the Risks of Cardioversion?

Although uncommon, cardioversion does have risks. The procedure can sometimes worsen arrhythmias. Rarely, it can cause life-threatening arrhythmias. These irregular heartbeats are treated with electrical shocks or medicines.

Cardioversion can dislodge blood clots in the heart. These clots can travel to organs and tissues in the body and cause a stroke or other problems. Taking anticlotting medicines before and after cardioversion can reduce this risk.

Clinical Trials

The National Heart, Lung, and Blood Institute (NHLBI) is strongly committed to supporting research aimed at preventing and treating heart, lung, and blood diseases and conditions and sleep disorders.

NHLBI-supported research has led to many advances in medical knowledge and care. Often, these advances depend on the willingness of volunteers to take part in clinical trials.

Clinical trials test new ways to prevent, diagnose, or treat various diseases and conditions. For example, new treatments for a disease or condition (such as medicines, medical devices, surgeries, or procedures) are tested in volunteers who have the illness. Testing shows whether a treatment is safe and effective in humans before it is made available for widespread use.

By taking part in a clinical trial, you can gain access to new treatments before they're widely available. You also will have the support of a team of health care providers, who will likely monitor your health closely. Even if you don't directly benefit from the results of a clinical trial, the information gathered can help others and add to scientific knowledge.

If you volunteer for a clinical trial, the research will be explained to you in detail. You'll learn about treatments and tests you may receive, and the benefits and risks they may pose. You'll also be given a chance to ask questions about the research. This process is called informed consent.

If you agree to take part in the trial, you'll be asked to sign an informed consent form. This form is not a contract. You have the right to withdraw from a study at any time, for any reason. Also, you have the right to learn about new risks or findings that emerge during the trial.

For more information about clinical trials related to cardioversion or arrhythmias, talk with your doctor. You also can visit the following Web sites to learn more about clinical research and to search for clinical trials:

For more information about clinical trials for children, visit the NHLBI's Children and Clinical Studies Web page.

Links to Other Information About Cardioversion

NHLBI Resources

Non-NHLBI Resources

Clinical Trials

May 25, 2012 Last Updated Icon

The NHLBI updates Health Topics articles on a biennial cycle based on a thorough review of research findings and new literature. The articles also are updated as needed if important new research is published. The date on each Health Topics article reflects when the content was originally posted or last revised.