Cardioversion is a procedure that uses a controlled electrical shock or medication to reset your heart back into a normal rhythm when you’re in atrial fibrillation (afib). It works by briefly interrupting the chaotic electrical signals in your heart’s upper chambers, giving your heart’s natural pacemaker a chance to take over again. Electrical cardioversion restores normal rhythm in about 92% to 96% of attempts, making it one of the most effective tools for stopping an afib episode.
How Cardioversion Resets Your Heart
During afib, electrical signals in your heart’s upper chambers fire rapidly and out of sync, creating a disorganized loop that sustains itself. Cardioversion delivers a brief burst of electricity that depolarizes most of the heart cells at once. Think of it as forcing a hard reset: by momentarily stopping all the chaotic signals, the heart’s natural pacemaker (a small cluster of cells called the sinus node) can resume its steady, coordinated rhythm.
This is different from defibrillation, which you might associate with cardiac arrest. Cardioversion delivers the shock in sync with your heartbeat, timed to a specific point in the cardiac cycle. That synchronization is what makes the procedure safe and controlled rather than an emergency jolt.
Electrical vs. Medication-Based Cardioversion
There are two approaches, and your doctor will choose based on how stable you are and how long you’ve been in afib.
Electrical cardioversion uses pads placed on your chest and back to deliver a shock, typically at 200 joules or more. It’s fast, highly effective, and is the preferred option when afib is causing low blood pressure, chest pain, or other signs of hemodynamic instability. It requires sedation, which is the main trade-off compared to the medication approach.
Pharmacological cardioversion uses an intravenous medication to restore rhythm without a shock. In the RAFF2 trial, about 52% of patients converted to normal rhythm with medication alone. For those who didn’t respond, electrical cardioversion was used as a follow-up step, bringing the overall success rate to 96%. Current guidelines recommend moving to electrical cardioversion rather than trying a second medication if the first drug doesn’t work.
For patients who are hemodynamically stable, both approaches are considered safe and effective. Electrical cardioversion is simply faster and more reliable on its own.
Blood Thinners Before and After
The biggest safety concern with cardioversion isn’t the shock itself. It’s the risk of dislodging a blood clot. Afib allows blood to pool in the upper chambers of your heart, and clots can form there, particularly in a small pouch called the left atrial appendage. When your heart snaps back to a normal rhythm, a clot can break loose and travel to the brain, causing a stroke.
To prevent this, the standard protocol requires at least three weeks of blood thinner therapy before cardioversion if your afib has lasted longer than 48 hours. After the procedure, you’ll continue blood thinners for a minimum of four weeks, regardless of whether you stay in normal rhythm. This post-procedure window matters because the upper chambers can be “stunned” after cardioversion, meaning they contract weakly for a period even after rhythm is restored. That temporary sluggishness creates ongoing clot risk.
Some newer blood thinners can shorten the pre-procedure timeline. Depending on which one you’re prescribed, cardioversion may be possible within 2 to 72 hours of starting the medication rather than waiting the full three weeks. Your care team may also use an imaging test (a transesophageal echocardiogram, where a small ultrasound probe is guided down your throat) to look directly at the heart chambers for clots. If the imaging is clear, cardioversion can sometimes proceed sooner. This imaging approach is particularly useful for patients with heart failure, high stroke risk, or those who haven’t been on blood thinners consistently.
What Happens During the Procedure
Electrical cardioversion is a brief outpatient procedure, usually lasting only a few minutes of active treatment. You’ll have an IV placed, and sticky electrode pads will go on your chest and back. A short-acting sedative is given through the IV so you’re asleep for the shock itself. Most people have no memory of it.
The electrodes are typically 8 to 12 centimeters in diameter and can be placed in one of two positions: front-to-back or front-to-side. Studies show comparable success rates with either placement. The doctor delivers the shock while monitoring your heart rhythm on a screen. If the first shock doesn’t convert the rhythm, additional shocks at higher energy levels may be tried, up to about three attempts.
The entire visit, including preparation and recovery monitoring, usually takes a few hours. You’ll need someone to drive you home because of the sedation.
Risks and Complications
Cardioversion complications are uncommon. The main risks include:
- Blood clots and stroke: The most serious risk, which is why the blood thinner protocol exists. With proper anticoagulation, this risk drops significantly.
- New rhythm disturbances: Rarely, the shock can trigger a different type of irregular heartbeat. These typically appear within minutes and are monitored for in the recovery period.
- Skin irritation or minor burns: The electrode pads can occasionally cause redness or superficial burns at the contact site. This is rare and resolves on its own.
How Long the Results Last
Cardioversion is effective at stopping an afib episode, but it doesn’t cure the underlying condition. The heart can slip back into afib days, weeks, or months later. In one study tracking patients after electrical cardioversion, about 38% had returned to afib within six months. That means roughly 6 in 10 patients maintained normal rhythm over that period, though individual results vary widely depending on how long you’ve had afib, the size of your heart chambers, and whether the underlying triggers are managed.
To improve the odds of staying in rhythm, many people take a heart rhythm medication after cardioversion. Addressing contributing factors like sleep apnea, high blood pressure, excess weight, and alcohol use also makes a meaningful difference in whether afib comes back. Some people undergo cardioversion more than once, and repeated procedures remain safe and effective when needed.
Who Is a Good Candidate
Cardioversion works best for people with recent-onset afib, meaning the episode started within the past few days to weeks. The longer your heart has been in afib, the harder it is to restore normal rhythm and the more likely it is to return. People with persistent afib lasting many months or years may still attempt cardioversion, but success rates decline and recurrence is more common.
For anyone whose afib is causing symptoms like shortness of breath, dizziness, fatigue, or chest discomfort, cardioversion offers the fastest path to relief. It’s also the first-line treatment when afib is making the heart pump too weakly, since restoring a normal rhythm immediately improves how well the heart moves blood.