A process in which an electronic device gives an electric shock to the heart. This helps reestablish normal contraction rhythms in a heart in cardiac arrest.


The heart has two upper chambers, the left atrium and the right atrium (collectively known as the atria), and two lower chambers the left and right ventricles.


When a heart is functioning normally it is said to be in sinus rhythm and is under the control of the hearts normal 'electrical centre' called the sinoatrial node.


When the ATRIA contracts at an excessively high rate and in an irregular way, the patient has ATRIAL FIBRILLATION. When the two lower chambers flutter and beat irregularly the patient has VENTRICULAR FIBRILLATION a condition far more serious the AF.


Ventricular Fibrillation:

This guidance refers to the treatment of Ventricular Fibrillation (VF), a devastating life-threatening condition. It is most commonly linked to heart attacks or muscle damage from previous heart attacks. Someone with VF generally collapses within seconds and within a very short space of time from when breathing and/or the pulse stops.


Cardiac arrest is potentially possible at any time whilst a patient is experiencing a 'heart attack', therefore the patient needs urgent medical attention by members of the public, first aiders, paramedics and hospital staff to try and avoid the possibility of cardiac arrest.



Cardioversion is a process that converts an arrhythmia back to sinus rhythm and uses an instrument called a defibrillator. The aim is to deliver electrical energy to the heart to stun the hearts momentarily and allow a normal sinus rhythm to 'kick in' via the sinoatrial node. The scientific evidence to support early defibrillation is overwhelming; the delay from collapse to delivery of the first shock is the single most important determinant of survival.


Evidence has shown us the earlier this shock is delivered the greater the chances of the heart re-establishing a heart beat. Defibrillators are electrical apparatus called AED (Automatic External Defibrillator).


An AED can be used safely and effectively without previous training. Therefore, the use of an AED should not be restricted to trained rescuers. However, training should be encouraged to help improve the time to shock delivery and correct pad placement.


If defibrillation is delivered promptly, survival rates as high as 75% have been reported. The chances of successful defibrillation decline at a rate of about 10% with each minute of delay; basic life support will help to maintain a shockable rhythm but is not a definitive treatment.



Automated External Defibrillators (AED) are now widely available in public places and are safe and reliable devices at analyzing VF and therefore lay people with little or no training can use them. For every one minute delay in delivering the shock, the chances of survival reduces by up to 10%.


Location of Defibrillators (AED):

Public access defibrillators can now be found in places including offices, shopping centres, airports, railways stations, sports centre's health clubs, workplaces and many other locations.

 Defib logo 

The use of this UK standardised AED sign is encouraged, to highlight the location of AED.







We hope you find this article useful. This is one in an alphabetical series of articles addressing various symptoms and their first aid treatments. If you would like more information on related resuscitation and first aid training, please get in touch.


You might also be interested in our news pages. We particularly like the British Heart Foundation's video with Vinnie Jones explaining CPR (see staying Alive article 26 January 2011).


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First Response. Training for life. Training to save a life.




*Source: Resuscitation Council (UK) 2010 Guidelines (The use of External Defibrillators: 2010:29).

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