What Is Cardioversion?

Your heart has just been caught racing or fluttering out of rhythm, and somewhere in the conversation your doctor says a word that sounds more alarming than it usually is: cardioversion. So what actually happens? In short, it is a planned, controlled electric shock, delivered through pads or paddles on the chest, that resets the heart's electrical system so its normal rhythm can take over again. The video at the top of this page, "Cardioversion of Atrial Fibrillation" (just under three minutes), puts it plainly: an electric current is used to reset the heart's rhythm back to its regular pattern — normal sinus rhythm. This article answers, one by one, the questions patients most often ask about it.

Which rhythms is it used for?

Cardioversion is a treatment for abnormal heart rhythms — arrhythmias — rather than for blocked arteries or weak heart muscle. It is most often used for atrial fibrillation and atrial flutter, where the upper chambers of the heart quiver or spin instead of beating in an organised way, and for some fast rhythms that start in the lower chambers. If you are living with atrial fibrillation, our guide to what atrial fibrillation is explains the rhythm itself in more detail. Whether cardioversion is the right tool depends on the rhythm, how long it has been present, and how it is affecting you — which is why an ECG tracing comes first, as our article on what an ECG shows describes.

Is it the same as the shock in an emergency?

Not quite, and the difference matters. The dramatic emergency shock — defibrillation — is given to someone whose heart has stopped beating effectively, and it is deliberately unsynchronised. Planned cardioversion is gentler and more precise: you are monitored, sedated, and the shock is timed (synchronised) to land at a safe point in the heart's electrical cycle. The second video on this page, "Electrical Cardioversion" (about a minute long), shows the equipment and set-up used. Same family of technology, very different circumstances — a booked procedure with a team around you, not a rescue.

What happens, step by step?

You will usually be asked not to eat or drink for a period beforehand, because of the sedation. In the procedure room, sticky monitoring leads are placed on your chest, and your heart rhythm, blood pressure, and oxygen levels are watched throughout. Large pads are placed on the chest — or a pad on the chest and one on the back — and a short-acting sedative is given through a vein so you sleep briefly and feel nothing of the shock itself. The clinician then delivers the controlled shock, the monitor is checked, and if the rhythm has not reset, a further shock at a higher energy may be tried. Most people wake within minutes remembering none of it, and the whole appointment is usually a matter of hours rather than an overnight stay.

Why do doctors talk about blood thinners around it?

Because an out-of-rhythm heart lets blood pool and potentially form clots, and restoring a strong beat can move a clot that has formed. For that reason, teams think carefully about blood-thinning treatment and, in some situations, a scan of the heart before the procedure — the exact plan depends on how long the rhythm has been abnormal and on your individual stroke risk. Clinicians often summarise that risk with a scoring system; you can see the factors involved in our CHA2DS2-VASc calculator. This is general information only, not a recommendation — your own team's plan is the one to follow.

Does it fix the problem for good?

Honestly, sometimes — and sometimes the rhythm drifts back over the following weeks or months, because cardioversion resets the rhythm without treating whatever triggered it. That is why it is often one step in a longer plan that can include rhythm-control medicines, treating triggers such as thyroid problems or sleep apnoea, or a procedure called ablation, which our guide to cardiac ablation explains. A successful cardioversion still tells your team something valuable: how you feel in a normal rhythm, which helps them judge whether keeping you there is worth pursuing.

References & further reading

• MedlinePlus — Cardioversion (Medical Encyclopedia)
• MedlinePlus — Atrial Fibrillation
• NHLBI — Atrial Fibrillation

MedicalVideos.com has published trusted medical videos since 2007. The site was founded by Dr. Mohamed Ibrahim, MD, PhD — physician-scientist.

Frequently Asked Questions

Does cardioversion hurt?

You are given a short-acting sedative beforehand and sleep through the shock itself, so people generally remember nothing of it. Afterwards the skin under the pads can feel sore or tender, like mild sunburn, for a day or two.

How long does the procedure take?

The shock itself takes seconds, and the procedure in the room is usually brief. Most of the appointment is preparation, monitoring, and recovery from the sedation, and people typically go home the same day.

Will I need to stay away from driving afterwards?

Because of the sedation, you should not drive for the rest of the day and will need someone to take you home. Your team will tell you exactly when you can drive and return to normal activities.

What if the shock does not work?

The team may try again at a higher energy during the same session. If the rhythm still does not reset, or returns later, your doctor will discuss other options such as medicines or ablation — cardioversion is one option among several, not a last resort.

Is cardioversion the same as a pacemaker?

No. Cardioversion is a one-off external treatment delivered through chest pads. A pacemaker is a small implanted device that continuously helps control the heart's rhythm over the long term.

This article is for general education only and is not medical advice. It does not replace consultation with a qualified clinician. If you have palpitations with chest pain, breathlessness, or faintness, seek urgent medical care.

Dr. Mohamed Ibrahim, MD, PhD

Physician-scientist · Founder, MedicalVideos.com

Dr. Ibrahim founded MedicalVideos.com in 2007 to make medical and surgical education freely accessible to students, clinicians, and patients.

Last reviewed: 11/12/26