Atrial Fibrillation (AFib)
The most common reason. Cardioversion is used to bring a fast, irregular rhythm back to normal, often when symptoms persist despite medication, or as a planned step in a rhythm-control strategy.
Medically Reviewed By: Dr Paul Lim – MBBS, M.Med (Int Med), MRCP (UK), FAMS (Cardiology)
Heart Rhythm Treatment
Electrical Cardioversion in Singapore
Electrical cardioversion is a short, planned procedure — also called DC (direct current) cardioversion or, in Chinese, 心脏电复律 (xīnzàng diàn fùlǜ) — that uses a brief, carefully timed electric shock to reset an abnormal heart rhythm back to a normal one. It is most often used for atrial fibrillation and atrial flutter, where the heart beats fast and irregularly. The shock is delivered while you are asleep under short sedation, so you do not feel it.
Dr Paul Lim Chun Yih
Senior Consultant Cardiologist & Electrophysiologist
Performed by Heart Rhythm Specialist
1,000+ Ablation & Device Procedures
Asleep Under Sedation — Painless
22+
Years of
Clinical Experience
Clinical Experience
Your Specialist
Procedure Performed by Dr Paul Lim
Senior Consultant Cardiologist & Cardiac Electrophysiologist
Dr Paul Lim subspecialises in heart rhythm disorders, performing cardioversion, catheter ablation, and pacemaker and defibrillator procedures for arrhythmia patients. He completed advanced fellowship training at Barts Heart Centre, London — one of Europe’s largest heart rhythm centres — under Singapore’s HMDP award.
UK & SG
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1,000+
Ablation & Device Procedures
The Procedure Explained
What Is Electrical Cardioversion?
Electrical cardioversion is a procedure that restores a normal heart rhythm by delivering a brief, controlled electric shock to the heart through pads placed on the chest. It is used when the heart is beating with a fast, abnormal rhythm — most commonly atrial fibrillation (AFib) or atrial flutter.
In a normal heart, each beat is triggered by an electrical signal from the heart’s natural pacemaker (the sinus node). In atrial fibrillation, disorganised electrical activity makes the upper chambers quiver instead of beating properly, so the heartbeat becomes fast and irregular. The cardioversion shock briefly interrupts this abnormal activity and gives the sinus node the chance to take over again, returning the heart to a normal (sinus) rhythm.
The shock is synchronised — the machine times it precisely to the heart’s own electrical cycle (the R wave) to deliver it safely. You are given short sedation or a brief general anaesthetic beforehand, so you are asleep and do not feel the shock. The procedure itself is very quick. Cardioversion treats the rhythm; it does not treat blocked arteries and is not a treatment for a heart attack.
A Common Question
Cardioversion vs Defibrillation — What’s the Difference?
People often confuse cardioversion with defibrillation because both use an electric shock, but they are used for different situations.
| Synchronised cardioversion | Defibrillation | |
|---|---|---|
| When it’s used | A planned procedure for an organised but abnormal fast rhythm (AFib, atrial flutter, SVT, or a stable fast rhythm from the lower chambers) | An emergency for a life-threatening, chaotic rhythm (ventricular fibrillation or pulseless ventricular tachycardia) — a cardiac arrest |
| Timing of the shock | Synchronised — timed to the heart’s own R wave to avoid the vulnerable part of the cycle | Unsynchronised — delivered immediately, as there is no organised rhythm to synchronise to |
| Energy | Usually lower energy | Usually higher energy |
| Is the patient awake? | No — given as a planned procedure under sedation | No — the person is unconscious in cardiac arrest |
| Setting | Elective, in a monitored procedure area | Emergency resuscitation |
In short: cardioversion is a planned, synchronised shock for an organised abnormal rhythm, while defibrillation is an emergency, unsynchronised shock for a cardiac arrest.
When It’s Needed
When Is Electrical Cardioversion Used?
Cardioversion is used to restore a normal rhythm when the heart is in a fast, abnormal rhythm — particularly when it causes symptoms such as palpitations, breathlessness, chest discomfort, tiredness, or dizziness. A specialist assessment, including an ECG, confirms the rhythm first. Common reasons include:
Atrial Flutter
A fast, more regular rhythm from the upper chambers, atrial flutter often responds well to cardioversion.
Supraventricular Tachycardia (SVT)
Selected fast rhythms arising from the upper chambers that do not settle with medication.
Some Ventricular Tachycardias
A fast rhythm from the lower chambers in a stable patient may be cardioverted under specialist care.
Cardioversion is not used for every rhythm problem. A persistently slow heartbeat is treated with a pacemaker, not a shock, and a chaotic rhythm in a collapsed patient (ventricular fibrillation) needs emergency defibrillation rather than planned cardioversion.
Been told you may need a cardioversion? Discuss your options with Dr Paul Lim.
Two Approaches
Electrical vs Chemical Cardioversion
There are two ways to convert an abnormal rhythm back to normal:
- Electrical (DC) cardioversion — a brief synchronised shock under sedation, as described on this page. It works quickly and has a high immediate success rate.
- Chemical (pharmacological) cardioversion — anti-arrhythmic medication, given by mouth or through a drip, used to coax the heart back into rhythm without a shock. It avoids sedation but is generally slower and less reliable than the electrical method, and the medicines have their own considerations.
The choice depends on the rhythm, how long it has been present, your heart’s condition, and your preferences. Your specialist will recommend the most suitable approach. The same rules about blood thinners (anticoagulation) apply to both methods.
Suitability & Safety
Am I Suitable, and Why Are Blood Thinners Important?
Your suitability is decided during a consultation based on your rhythm, symptoms, how long the abnormal rhythm has been present, and your overall heart health.
The most important safety step is preventing a stroke. When the heart has been in atrial fibrillation or flutter for more than about 48 hours, a small blood clot can form in the upper chamber. Restoring a normal rhythm can dislodge that clot and cause a stroke. To prevent this, current European Society of Cardiology (ESC) guidelines for atrial fibrillation recommend one of the following before an elective cardioversion:
- At least three weeks of effective anticoagulation (blood-thinning medication) beforehand, or
- A transoesophageal echocardiogram (TOE / TEE) — an ultrasound scan from inside the gullet (oesophagus) that looks directly at the heart to confirm there is no clot, allowing cardioversion to proceed sooner.
Anticoagulation is then continued for at least four weeks afterwards, and often long term, depending on your individual stroke risk (assessed with the CHA₂DS₂-VASc score).
Cardioversion may be less suitable, or need extra preparation, if there is an untreated clot, a very enlarged upper chamber, an uncorrected cause (such as an overactive thyroid or a significant electrolyte imbalance), or if previous cardioversions have not held — in which case catheter ablation or a medication strategy may be discussed instead.
Step by Step
How Electrical Cardioversion Is Performed
Electrical cardioversion is a short procedure carried out in a monitored area with an anaesthetist or sedation specialist present. It is not surgery and involves no cuts.
Before the procedure: You will usually be admitted on the day after fasting for about 6 hours. Your blood-thinning medication and a recent blood test are checked to confirm it is safe to proceed. A TOE scan may be done first if needed (see above). Adhesive pads are placed on your chest (and sometimes your back).
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1
Preparation and monitoring
You lie on a trolley with ECG, blood-pressure, and oxygen monitoring attached, and a small drip is placed in a vein.
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2
Sedation
A short-acting sedative or brief general anaesthetic is given through the drip. You fall asleep within moments and are not aware of the shock.
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3
The synchronised shock
Once you are asleep, the cardiologist delivers a synchronised shock through the chest pads. If the first shock does not restore a normal rhythm, one or more further shocks at a higher energy may be given.
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4
Waking up
You wake within minutes of the shock. The whole procedure usually takes only about 15 to 30 minutes from sedation to waking.
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5
Recovery and observation
You rest and are monitored while the sedation wears off, with an ECG to confirm the rhythm. You stay overnight and go home the next day.
What to Expect Afterwards
Cardioversion Recovery Timeline
Most patients recover quickly. Here is what to expect after an uncomplicated electrical cardioversion.
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1First few hours
Recovery from sedation
You rest while the sedation wears off. Mild drowsiness is normal. Some people have temporary redness or mild soreness on the chest where the pads were placed.
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2Day 1 — Discharge
Home the next day
Most patients are monitored, stay overnight, and go home the next day once the rhythm and observations are satisfactory.
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3First 24 hours
Sedation precautions
Because of the sedation, do not drive, operate machinery, sign important documents, or drink alcohol. Have someone stay with you.
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4Within a day or two
Back to normal activity
Most people return to normal activities and desk-based work quickly.
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5Ongoing
Medication and follow-up
Continue your blood thinners and any rhythm medication exactly as prescribed — this is essential for at least four weeks, and often longer. A follow-up reviews your rhythm and medication.
What to Expect
How Well Does Cardioversion Work?
Electrical cardioversion restores a normal rhythm immediately in the great majority of cases — the initial success rate for atrial fibrillation is high. However, cardioversion resets the rhythm; it does not cure the underlying tendency to the arrhythmia, so the abnormal rhythm can return over weeks or months in a proportion of patients.
To help the heart stay in a normal rhythm afterwards, your specialist may recommend:
- Anti-arrhythmic medication to help maintain the normal rhythm.
- Treating the underlying drivers — for example, managing blood pressure, sleep apnoea, thyroid problems, alcohol intake, and weight.
- Catheter ablation as a longer-term rhythm-control option if the arrhythmia keeps coming back, or if a more durable solution is preferred. (See our catheter ablation page.)
If the rhythm does return, cardioversion can often be repeated, and your specialist will review the overall plan with you.
Honest Expectations
Is Cardioversion Safe? Risks and Complications
Electrical cardioversion is a common, well-established, and generally low-risk procedure. Serious complications are uncommon, and death from the procedure itself is very rare. The main risks are:
- Stroke — the most important risk, caused by dislodging a clot. This is minimised by the blood-thinner and TOE precautions described above, which is why they are essential.
- Skin irritation or, rarely, minor burns where the pads are placed — usually mild and short-lived.
- Temporary irregular heartbeats immediately after the shock, which usually settle on their own; a slow heartbeat is occasionally seen.
- Risks related to the sedation or anaesthetic — generally minor in suitable patients and managed by the anaesthetist.
- The rhythm not converting, or returning — sometimes a normal rhythm cannot be restored, or the abnormal rhythm comes back later.
Dr Lim will discuss your individual risks and obtain written informed consent before the procedure.
Have questions about cardioversion? Dr Paul Lim is happy to help.
How It Compares
Cardioversion vs Ablation and Other Treatments
Cardioversion is one of several ways to manage an abnormal heart rhythm. Here is how it compares with the main alternatives.
| Treatment | What it does | When it is used | How it differs from cardioversion |
|---|---|---|---|
| Electrical cardioversion | A synchronised shock that resets an abnormal rhythm to normal | A planned reset of AFib, atrial flutter, or selected fast rhythms | Quick and effective at restoring rhythm, but does not stop the arrhythmia returning |
| Chemical (drug) cardioversion | Medication used to restore a normal rhythm without a shock | Selected cases, often newer-onset AFib | Avoids sedation but is generally slower and less reliable |
| Catheter ablation | Neutralises the small areas of heart tissue driving the abnormal rhythm | Recurrent or troublesome AFib, flutter, SVT, or VT, or when a longer-term solution is preferred | Aims to prevent the arrhythmia returning, rather than just resetting it. |
| Rate-control medication | Slows the heart rate without restoring a normal rhythm | When controlling the rate is the goal rather than restoring rhythm | Manages symptoms but leaves the heart in the abnormal rhythm |
| Pacemaker | Prevents the heart beating too slowly | Slow heart rhythms (bradycardia, heart block) | Treats a slow heartbeat, not a fast one — the opposite problem. (See our pacemaker page.) |
The right option depends on your specific rhythm, how often it occurs, your heart’s condition, and your preferences. Dr Paul Lim will discuss which approach is most appropriate for you.
Paying for Your Procedure
Electrical Cardioversion Cost & Insurance in Singapore
MOH surgeon fee benchmark (TOSP SD727H, synchronised cardioversion)
S$599.50 – 1,635
Published by Singapore’s Ministry of Health for synchronised
cardioversion, inclusive of GST (that is S$550 to S$1,500 before GST).
View MOH benchmark →
- MediSave claimable Synchronised cardioversion falls under MOH-approved surgical limits.
- Integrated Shield Plans (IP) Generally covered under inpatient hospital benefits, subject to plan terms. We can help verify your coverage before admission.
- Pre-authorisation support Our clinic team can assist with insurance pre-authorisation and required paperwork, and provide an itemised estimate before your procedure.
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Common Questions
Electrical Cardioversion FAQ
Answers to the questions patients ask most often about cardioversion, the procedure, and what to expect afterwards.
What is electrical cardioversion?
Electrical cardioversion is a short, planned procedure that uses a brief, synchronised electric shock to reset an abnormal heart rhythm — most often atrial fibrillation or flutter — back to a normal rhythm. You are asleep under sedation, so you do not feel the shock.
What is the difference between cardioversion and defibrillation?
Both use an electric shock, but cardioversion is a planned, lower-energy shock that is synchronised to the heartbeat to treat an organised abnormal rhythm. Defibrillation is an emergency, unsynchronised, higher-energy shock used to treat a cardiac arrest.
Are you awake during cardioversion?
No. You are given short-acting sedation or a brief general anaesthetic, so you are asleep for the shock and do not feel or remember it. You wake up within a few minutes.
Does cardioversion hurt?
No. Because you are asleep under sedation, you do not feel the shock. Afterwards, some people have mild redness or soreness on the chest where the pads were placed, which soon settles.
How long does a cardioversion procedure take?
The shock itself takes only seconds. From sedation to waking up, the procedure usually takes about 15 to 30 minutes. You then rest while the sedation wears off and stay overnight before going home.
Can you die during cardioversion?
Electrical cardioversion is a common, low-risk procedure, and death from the procedure itself is very rare. The most important risk is stroke from a dislodged blood clot, which is why blood thinners and, where needed, a TOE scan are used beforehand to make it as safe as possible.
Why do I need blood thinners before and after cardioversion?
If the heart has been in an abnormal rhythm for more than about 48 hours, a blood clot can form in the upper chamber. Restoring a normal rhythm could dislodge it and cause a stroke. Blood thinners for at least three weeks before (or a TOE scan to exclude a clot) and at least four weeks after greatly reduce this risk.
What is a TOE (TEE) and why might I need one before cardioversion?
A transoesophageal echocardiogram is an ultrasound scan taken from inside the gullet to look directly at the heart. It can confirm there is no clot in the upper chamber, allowing cardioversion to go ahead sooner than waiting three weeks on blood thinners.
How successful is cardioversion?
Electrical cardioversion restores a normal rhythm immediately in the great majority of cases. However, it resets the rhythm rather than curing the underlying tendency, so the abnormal rhythm can return in some patients. Medication or catheter ablation may be used to help maintain a normal rhythm.
How long will I stay in normal rhythm after cardioversion?
This varies. Some people stay in a normal rhythm for a long time; in others the arrhythmia returns within weeks or months. Anti-arrhythmic medication, treating underlying causes, and sometimes catheter ablation can help the rhythm last longer.
What should I avoid after cardioversion?
For the first 24 hours after the sedation, do not drive, operate machinery, sign important documents, or drink alcohol, and have someone stay with you. Most importantly, keep taking your blood thinners and rhythm medication exactly as prescribed.
Can cardioversion be repeated?
Yes. If the abnormal rhythm returns, cardioversion can usually be repeated. Your specialist will also review whether a different long-term approach, such as catheter ablation, would suit you better.
What is the difference between cardioversion and ablation?
Cardioversion resets the rhythm with a shock but does not stop the arrhythmia coming back. Catheter ablation treats the heart tissue causing the abnormal rhythm, aiming to prevent it returning. They are sometimes used at different stages of the same patient’s care.
How much does electrical cardioversion cost in Singapore?
The MOH surgeon fee benchmark for synchronised cardioversion (TOSP SD727H) is S$599.50 – S$1,635 with GST (S$550 – S$1,500 before GST). The anaesthetist fee, facility charge, any TOE scan, and medication are billed separately. Cardioversion is MediSave claimable and usually covered by Integrated Shield Plans. View MOH benchmark →