Cardioversion restores a normal heart rhythm using either a controlled electrical shock or medication delivered through an IV. The entire visit typically takes four to six hours, though the procedure itself lasts only a few minutes. Most people go home the same day.
There are two types: electrical cardioversion, which uses paddles or pads on your chest to deliver a precisely timed shock, and pharmacological (drug-based) cardioversion, which uses IV medications to reset the rhythm chemically. Both are highly effective, with success rates above 90% for converting irregular rhythms like atrial fibrillation back to a normal pattern.
Electrical vs. Drug-Based Cardioversion
Electrical cardioversion delivers a brief shock through pads placed on your chest. The shock is synchronized to your heartbeat so it lands at exactly the right moment in the heart’s electrical cycle, avoiding the vulnerable window that could trigger a dangerous rhythm. This synchronization is what distinguishes cardioversion from defibrillation, which delivers an unsynchronized shock during cardiac arrest.
Drug-based cardioversion skips the shock entirely. Instead, a medication is infused through an IV over about 30 minutes to coax the heart back into rhythm. In a large randomized trial comparing the two approaches in emergency department patients with acute atrial fibrillation, about 52% of patients converted to a normal rhythm with the drug infusion alone, avoiding the need for sedation and electrical shock altogether. When shocks were added for those who didn’t respond to the drug, 96% achieved normal rhythm. The shock-only group had a 92% success rate. Both strategies were safe, with no serious adverse events during follow-up.
The practical difference matters. Drug-based cardioversion doesn’t require sedation, which makes it simpler and less resource-intensive. Electrical cardioversion requires sedation but works faster and slightly more reliably. Your care team chooses between them based on how long your rhythm has been abnormal, your overall health, and the clinical setting.
What Happens Before the Procedure
The most important preparation happens weeks before the procedure itself: blood thinners. If your heart has been out of rhythm for more than 48 hours (or if no one is sure when it started), you’ll need at least three weeks of anticoagulation therapy beforehand. An irregular rhythm lets blood pool in the upper chambers of the heart, and pooled blood can form clots. Shocking the heart back into a normal rhythm can dislodge those clots, potentially sending them to the brain and causing a stroke.
In some cases, your doctor may order an imaging test where a small ultrasound probe is guided down your esophagus to get a close-up view of the heart’s upper chambers. This approach can detect clots that a standard ultrasound through the chest wall might miss. If no clots are found, cardioversion can sometimes proceed without the full three weeks of blood thinners. If clots are present, the procedure is postponed until they resolve.
On the day of the procedure, you’ll typically be asked to fast for several hours beforehand because of the sedation involved. An IV line is placed, and monitoring equipment tracks your heart rhythm, blood pressure, and oxygen levels throughout.
During Electrical Cardioversion
Once you’re connected to monitors, adhesive electrode pads are placed on your chest (and sometimes your back). These serve double duty: they deliver the shock and let the machine read your heart’s electrical activity in real time.
Before the shock, you receive sedation through your IV. This puts you into a brief, light sleep so you don’t feel the shock. The sedation typically lasts only a few minutes. You won’t remember the shock itself.
With you sedated, the machine is set to “synchronized” mode, meaning it tracks your heartbeat and times the shock to land during a specific safe point in each cardiac cycle. The energy level depends on the type of irregular rhythm being treated. For atrial fibrillation and atrial flutter, the starting energy is typically 200 joules. For other types of fast rhythms, it may start lower at around 100 joules.
The doctor presses the button, and the shock is delivered in a fraction of a second. Your body may jerk slightly from the muscle contraction. If the first shock doesn’t restore normal rhythm, additional shocks can be delivered at equal or higher energy levels, with the machine re-synchronized between each attempt. Most people need only one or two shocks. The success rate for restoring normal rhythm is greater than 95%.
During Drug-Based Cardioversion
If your team opts for the medication route, the process is quieter. You stay awake while the drug is infused through your IV, typically over about 30 minutes. Your heart rhythm is monitored continuously on a screen. If the medication works, you’ll see the rhythm shift on the monitor, sometimes within minutes of the infusion completing.
If the drug doesn’t convert your rhythm, your team may proceed with electrical cardioversion as a follow-up step. This combined approach (try the drug first, then shock if needed) is common in emergency settings and achieves very high overall success rates.
Risks and Complications
Cardioversion is considered a low-risk procedure. The most significant danger is blood clots breaking free and traveling to the brain or lungs, which is why the anticoagulation preparation is so important. Stroke and pulmonary embolism are rare when blood thinners are used properly before and after the procedure.
Other complications are uncommon. Some people develop a different type of irregular rhythm during or immediately after the shock, though this is rare and usually resolves quickly under monitoring. Minor skin irritation or small burns at the electrode pad sites can occur but are also rare. The sedation carries its own small risks, similar to any brief anesthesia.
Recovery and What Comes After
After the shock, you’ll wake up from sedation within minutes. Most people feel groggy or slightly confused for a short time. The medical team monitors your heart rhythm and vital signs as you recover, and the total time from arrival to discharge is typically four to six hours.
You won’t be able to drive for 24 hours after the procedure because of the sedation, so you’ll need someone to take you home. Some people notice mild chest soreness or skin redness where the pads were placed, but this fades within a day or two.
The critical aftercare step is continuing blood thinners for at least four weeks after cardioversion. Even though your heart is back in normal rhythm, the upper chambers can remain sluggish for a period afterward, creating ongoing clot risk. The elevated chance of blood clots, combined with the fact that atrial fibrillation frequently recurs in the weeks following the procedure, is why this post-procedure anticoagulation window exists. Your doctor will determine whether you need blood thinners beyond that four-week minimum based on your individual stroke risk factors.
There is no guaranteed timeline for how long the corrected rhythm will last. Some people maintain normal rhythm for years. Others experience a return of atrial fibrillation within weeks or months and may need repeat cardioversion, medication to maintain rhythm, or other treatments like catheter ablation.