Cardioversion is a method to restore a rapid heart beat back to normal. Cardioversion is used in persons who have heart rhythm problems (arrhythmias), which can cause the heart to beat too fast. Cardioversion can be done using electric shock (electric cardioversion) or medications (pharmacologic cardioversion).

Electrical Cardioversion

Electric cardioversion uses a device that can be placed inside (external) or outside (internal) the body.
An external cardioversion is often done during an emergency situation. External cardioversion uses a device called a defibrillator. When the defibrillator paddles are placed on your chest, a shock is delivered to your heart. This shock causes the heart rate to return to a normal rhythm.

People who have a recent arrhythmia (usually atrial fibrillation) or one that can not be controlled with medicines may be scheduled for external cardioversion. This is usually done for patients who are young or  intolerant of atrial fibrillation because of symptoms or decreased work capacity. Before this is done, tests such as a transoesophageal echocardiogram are often done to make sure that there are no blood clots in the heart. This involves swallowing a thin ultrasound probe (similar to a gastroscopy), and it enables cardiologists to examine the heart for blood clots. If Blood clots are found then cardioversion is unsafe to perform. If you are having a scheduled cardioversion, you will usually be given a sedative or given a general anaesthetic before the cardioversion procedure starts.

After the procedure, you may be given medicine to prevent blood clots (like warfarin)and help prevent the arrhythmia from coming back.

Pharmacological Cardioversion

Cardioversion can be done using drugs that are taken by mouth or given through an intravenous line (IV). It can take several minutes to days for a successful cardioversion. If pharmacological cardioversion is done in a hospital, your heart rate will be regularly checked. Cardioversion using drugs can be done outside the hospital, but this requires close follow-up with a cardiologist. Usually the cardiologist will perform an transthoracic or transoesopheal echo to assess the heart before considering pharmacological cardioversion.

As with electrical cardioversion, blood thinning medicines may be given to prevent blood clots from moving to the heart.


Possible complications of cardioversion are uncommon, but may include:

  • Worsening of the arrhythmia
  • Blood clots that can cause a stroke or other organ damage
  • Bruising, burning, or pain where the paddles were used
  • Allergic reactions from medicines used in pharmacologic cardioversion

Those who perform external cardioversion may be shocked if the procedure is not done correctly. This can cause heart rhythm problems, pain, even death.

Update Date: 7/12/2006

Updated by: Glenn Gandelman, M.D., M.P.H., Assistant Clinical Professor of Medicine, New York Medical College, Valhalla, NY. Review provided by VeriMed Healthcare Network.