An automated external defibrillator (AED) is a portable, lightweight medical device designed to deliver a controlled electric shock to the heart to restore a normal cardiac rhythm during cardiac arrest caused by ventricular fibrillation or pulseless ventricular tachycardia. AEDs are specifically designed for use by non-medical bystanders with minimal or no prior training, making them a critical component of the chain of survival for out-of-hospital cardiac arrest.
When switched on, an AED provides clear, audible voice instructions that guide the user step by step through the entire process. The device automatically analyses the heart’s electrical rhythm through adhesive electrode pads placed on the patient’s bare chest. If a shockable rhythm is detected, the AED charges to the appropriate energy level and instructs the user to press a shock button (fully automated AEDs deliver the shock without user action). The device will not advise a shock for non-shockable rhythms, making it safe to use by anyone. High-quality CPR should be continued between AED analyses.
Public access defibrillators are installed in many locations throughout the UK, including transport hubs, shopping centres, sports venues, schools, and community buildings. Their locations can be found via the British Heart Foundation’s national AED register or via the 999 call handler, who can direct a caller to the nearest device while sending an ambulance. Local schemes register AEDs with ambulance services so that trained volunteers can be alerted by text when a cardiac arrest is reported nearby.
For cardiac arrest survivors and their families, knowledge of local AED locations and confidence in how to use one provides both reassurance and practical preparedness. Many survivors encourage family members to attend CPR and AED training, and SCA UK supports initiatives to increase public access to defibrillators across the UK.