Cardioversion is a medical procedure that resets an abnormal heart rhythm back to its normal, steady pattern. It’s most commonly used for atrial fibrillation, a condition where the upper chambers of the heart quiver chaotically instead of beating in rhythm. There are two forms: electrical cardioversion, which delivers a controlled shock through the chest, and pharmacological cardioversion, which uses medication to restore normal rhythm.
Why Cardioversion Is Done
The heart has a built-in electrical system that coordinates each beat. When that system misfires, the heart can fall into an abnormal rhythm. Cardioversion is used to treat several of these rhythm problems, including atrial fibrillation, atrial flutter, and certain types of rapid heartbeat originating above the lower chambers of the heart (supraventricular tachycardia).
Atrial fibrillation is by far the most common reason. When the upper chambers of the heart quiver instead of contracting properly, blood doesn’t move through the heart efficiently. This can cause symptoms like fatigue, shortness of breath, dizziness, and a fluttering sensation in the chest. Cardioversion aims to snap the heart back into its normal coordinated rhythm, called sinus rhythm.
If an abnormal rhythm is causing dangerously low blood pressure or other signs that the heart isn’t pumping enough blood, electrical cardioversion is the first-line treatment. In less urgent situations, your doctor may recommend either the electrical or medication-based approach depending on how long the abnormal rhythm has been going on and your overall health.
Electrical vs. Medication-Based Cardioversion
Electrical cardioversion uses a brief, precisely timed shock delivered through pads placed on your chest. The shock interrupts the chaotic electrical signals and gives your heart’s natural pacemaker a chance to take over again. Success rates are high, restoring normal rhythm in 80 to 90% of cases. For atrial flutter specifically, it works even better and requires less energy than for atrial fibrillation.
Pharmacological (medication-based) cardioversion skips the shock entirely. Instead, you receive an antiarrhythmic drug, typically through an IV, that chemically coaxes the heart back into normal rhythm. It’s simpler in some ways because it doesn’t require sedation or an anesthesia team. The tradeoff is a notably lower success rate of roughly 50%, and the medications themselves can cause side effects. This approach works best for episodes of atrial fibrillation that started recently or that tend to stop on their own.
In some cases, doctors try medication first and move to electrical cardioversion if it doesn’t work.
What Happens Before the Procedure
One of the biggest concerns with cardioversion is blood clots. When the heart’s upper chambers aren’t beating properly, blood can pool and form clots, particularly in a small pouch called the left atrial appendage. If cardioversion suddenly restores normal rhythm, a clot sitting there could be pumped out into the bloodstream and travel to the brain, causing a stroke.
To reduce this risk, current guidelines from the American Heart Association recommend at least three weeks of blood-thinning medication before cardioversion if your abnormal rhythm has lasted more than two days. After the procedure, you’ll typically continue blood thinners for at least four more weeks, because the heart’s upper chambers can remain sluggish during that recovery window even after normal rhythm returns.
If waiting three weeks isn’t practical, your doctor can check for clots using a specialized ultrasound called a transesophageal echocardiogram. A small probe is passed down your throat to get a close-up view of the back of the heart, where clots are most likely to hide. If no clots are found, cardioversion can proceed sooner.
What to Expect During Electrical Cardioversion
The procedure itself is quick, often taking only a few minutes of active treatment. You’ll have an IV placed, and adhesive electrode pads will be positioned on your chest (and sometimes your back). Because the shock can be uncomfortable, you’ll receive sedation through the IV so you’re briefly asleep during the actual moment of the shock.
The medical team starts with a set energy level and increases it if the first attempt doesn’t work. A common approach uses a sequence starting at 200 joules and escalating to 300, then 360 joules if needed. Your heart rhythm is monitored continuously, and the shock is precisely synchronized to a specific point in your heartbeat to avoid triggering a more dangerous rhythm.
How Timing Affects Success
The longer your heart has been in an abnormal rhythm, the harder it is to reset. Data on electrical cardioversion for atrial fibrillation shows a clear pattern: episodes lasting zero to three days convert successfully about 77% of the time. That drops to around 66% for episodes lasting four days to three months, and falls further to about 60% for episodes persisting beyond three months. This is one reason doctors often encourage cardioversion sooner rather than later when a rhythm control strategy is chosen.
Risks and Complications
Cardioversion is considered safe, but it’s not risk-free. The most serious concern is stroke. A large nationwide study found that about 1% of patients experienced a stroke within the year following elective cardioversion. The risk is concentrated in the first two weeks after the procedure, when stroke rates are roughly seven and a half times higher than during the rest of the year. This is precisely why the blood-thinning protocol before and after the procedure is so important.
Other possible complications include skin irritation or mild burns at the electrode pad sites, and in rare cases, the heart can briefly pause after the shock before resuming its normal rhythm. Some people experience a temporary drop in blood pressure from the sedation. There’s also a chance the procedure simply doesn’t work, or that it works initially but the abnormal rhythm returns days to weeks later.
Recovery After Cardioversion
Because you receive sedation, you’ll feel drowsy afterward and won’t be able to drive for 24 hours. You’ll need a responsible adult to take you home. Most people feel back to normal within a day or so, though some notice mild chest soreness where the pads were placed. Your doctor will let you know when you can return to work and normal activities, which for many people is the next day.
The weeks after cardioversion matter as much as the procedure itself. You’ll stay on blood thinners for at least four weeks, and your doctor may prescribe an antiarrhythmic medication to help your heart maintain its restored rhythm. Even with these precautions, atrial fibrillation recurs in a significant number of people over time, and some may need repeat cardioversion or alternative treatments like catheter ablation down the line.