Cardioversion (KAR-de-o-VER-shun) is a procedure that can restore a fast or irregular heartbeat to a normal rhythm. A fast or irregular heartbeat is called an arrhythmia (ah-RITH-me-ah).
To understand arrhythmias, it helps to understand how the heart works. Your heart is a muscle; it has an internal electrical system that controls the rate and rhythm of your heartbeat. With each heartbeat, an electrical signal spreads from the top of your heart to the bottom.
As the signal travels, it causes your heart to contract and pump blood. The process repeats with each new heartbeat. (For more information about the heart's electrical system and a detailed animation, go to the Health Topics How the Heart Works article.)
A problem with any part of this process can cause an arrhythmia. During an arrhythmia, the heart can beat too fast, too slow, or with an irregular rhythm. Doctors use cardioversion to correct fast or irregular heartbeats.
Cardioversion is done two ways: using an electrical procedure or using medicines.
For the electrical procedure, your heart is given low-energy shocks to trigger a normal rhythm. You're temporarily put to sleep before the shocks are given. This type of cardioversion is done in a hospital as an outpatient procedure. "Outpatient" means you can go home after the procedure is done.
Using medicines to correct arrhythmias also is a form of cardioversion. This type of cardioversion usually is done in a hospital, but it also can be done at home or in a doctor's office.
This article only discusses the electrical cardioversion procedure.
Cardioversion isn't the same as defibrillation (de-fib-rih-LA-shun), although they both involve shocking the heart. Defibrillation gives high-energy shocks to the heart to treat very irregular and severe arrhythmias. It's used to restore normal heartbeats during life-threatening events, such as sudden cardiac arrest.
The success rate of cardioversion depends on the type of arrhythmia it’s used to treat. However, with all arrhythmias, the success rate is usually 75 percent or better.
Fast or irregular heartbeats can occur again after cardioversion. For this reason, you may need to have more than one cardioversion over time.
The procedure has some risks. For example, it may worsen arrhythmias. However, serious problems are rare.