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Cardioversion is a method to restore an abnormal heart rhythm back to normal.


Cardioversion can be done using an energy shock (electric cardioversion) or medications (pharmacologic cardioversion).


Electric cardioversion may use a device that can be placed inside (internal) or outside (external) the body.

External electric cardioversion uses a device called a defibrillator. Electrode patches are placed on the front and back of the chest and connected to the defibrillator. When the defibrillator paddles are placed on your chest, an energy shock is delivered to your heart. This shock interrupts all existing electrical activity of the heart and then allows the normal heart rhythm to return.

Reasons you may have external electric cardioversion:

  • An external cardioversion may be done during an emergency situation. Some abnormal rhythms, such as ventricular tachycardia or ventricular fibrillation, can be life threatening. An energy shock can be life saving.
  • People who have an arrhythmia (usually atrial fibrillation) that began recently, or one that cannot be controlled with medicines, may be scheduled for external cardioversion. First, tests such as a transesophageal echocardiogram are often done to make sure that there are no blood clots in the heart. Some people may need to take blood thinners before the cardioversion procedure. If you are having a scheduled cardioversion, you will usually be given a sedative before the procedure starts.

After the external cardioversion, you may be given medicine to prevent blood clots and to help prevent the arrhythmia from coming back.

Internal cardioversion uses a device called an implantable cardioverter defibrillator (ICD). ICDs have two parts: a pulse generator and electrodes (wires). The generator is implanted under the skin, like a pacemaker. The wires connect the generator to the heart. This device also delivers an electric shock to your heart. An implantable cardiac defibrillator is placed in people who are at high risk of sudden cardiac death from dangerous arrhythmias such as ventricular tachycardia or ventricular fibrillation.

See also: Implantable cardiac defibrillator


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 pharmacologic cardioversion is done in a hospital, your heart rate will be regularly checked. Although rare, cardioversion using drugs can be done outside the hospital. However, this requires close follow-up with a cardiologist.

As with electrical cardioversion, you may be given blood thinning medicines to prevent blood clots from forming and leaving the heart (which can cause a stroke).


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 electrodes 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.


Miller JM, Zipes DP. Therapy for cardiac arrhythmias. In: Libby P, Bonow RO, Mann DL, Zipes DP. Braunwald's Heart Disease: A Textbook of Cardiovascular Medicine. 8th ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 33.

Epstein AE, DiMarco JP, Ellenbogen KA, Estes NA 3rd, Freedman RA, Gettes LS, et al. ACC/AHA/HRS 2008 guidelines for device-based therapy of cardiac rhythm abnormalities: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Writing Committee to Revise the ACC/AHA/NASPE 2002 Guideline Update for Implantation of Cardiac Pacemakers and Antiarrhythmia Devices): developed in collaboration with the American Association for Thoracic Surgery and Society of Thoracic Surgeons. Circulation. 2008;117:e350-e408.

Review Date: 4/23/2009
Reviewed By: Steven Kang, MD, Division of Cardiac Pacing and Electrophysiology, East Bay Arrhythmia, Cardiovascular Consultants Medical Group, Oakland, CA. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.
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