Automated External Defibrillators are used to treat cardiac arrest and are designed so that anyone - even an ordinary passer-by - can use them. AEDs deliver an electric shock to the heart of the victim, which can help restore a normal heart rhythm by shocking it out of the irregular and uncordinated contractions (fibrillation) associated with cardiac arrest. Until normal heart rhythm is restored, the victim must also be given CPR (chest compressions). However, CPR alone will not revive a cardiac arrest victim: to survive, they must be defibrillated as soon as possible.