Imagine you're at a bustling café, and someone nearby collapses. Panic spreads. Someone calls 999. But in that moment — before paramedics arrive — there's a crucial tool that could mean the difference between life and death: the defibrillator.
You’ve likely seen one on a wall at a train station or leisure centre, or heard about them in TV dramas. But what exactly do defibrillators do? And why are they such a critical part of the emergency response toolkit? In this guide, we break it down for UK readers — clearly, accurately, and without the fluff.
What Is a Defibrillator?
A defibrillator is a device that delivers a high-energy electric shock to a person’s heart in the event of a life-threatening arrhythmia or sudden cardiac arrest (SCA). This shock is called defibrillation, and its goal is to restore a normal heartbeat.
Defibrillators come in two main types:
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Automated External Defibrillators (AEDs) – Designed for use by members of the public with no medical training
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Manual Defibrillators – Used by healthcare professionals in hospitals or by paramedics
What Happens During Sudden Cardiac Arrest?
SCA is an electrical malfunction of the heart, causing it to stop pumping blood effectively. It is not the same as a heart attack (which is usually due to a blockage — a plumbing issue). If a heart attack is a plumbing problem, sudden cardiac arrest is an electrical failure — the system short-circuits and the heart stops beating effectively.
Two of the most common shockable arrhythmias are:
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Ventricular Fibrillation (VF): A disorganised, quivering rhythm that prevents effective pumping
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Ventricular Tachycardia (VT): A very fast rhythm that may or may not produce a pulse
Without rapid treatment, brain damage can begin within 3–5 minutes, and death can occur in less than 10 minutes.
How Defibrillators Work
Defibrillators deliver a controlled electric shock that temporarily stops the heart’s abnormal rhythm, giving it a chance to restart in a normal pattern. It’s often compared to rebooting a computer — stopping the malfunction to allow a reset.
AEDs take the guesswork out of this process. They analyse the patient’s heart rhythm and determine whether a shock is needed. If no shockable rhythm is detected, the AED will not deliver a shock — so there’s no danger of doing harm.
Step-by-Step: How to Use an AED
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Call 999 first – Always alert emergency services.
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Turn on the AED – Most units have a prominent ON button.
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Follow voice instructions – The device will guide you step-by-step.
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Attach electrode pads – Place them on the chest as illustrated.
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Let the AED analyse – It will assess the heart rhythm.
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Deliver a shock if advised – Ensure no one is touching the person.
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Continue CPR – Follow prompts until help arrives.
AEDs are designed to be simple, safe, and effective. Training is encouraged but not required — though product familiarisation is always advisable, even for trained responders.
Why AEDs Are in Public Places
Public-access AEDs are becoming more common across the UK, and for good reason. Immediate use of a defibrillator can raise survival rates to over 70% if used within the first 3 minutes of collapse.
That’s why you’ll find AEDs in airports, shopping centres, train stations, offices, schools, and sports venues. They're as vital as fire extinguishers — and just as important to keep maintained.
The UK’s national AED database, The Circuit, helps emergency services locate the nearest defibrillator when someone calls 999. With over 80,000 devices now registered, response times are improving nationwide.
In some cases, bystanders may be guided by ambulance control to the nearest AED and talked through how to use it — meaning the chain of survival begins even before responders arrive.
AEDs and CPR: Working Together
Defibrillators are only one part of the response. CPR (cardiopulmonary resuscitation) keeps oxygenated blood flowing to the brain and organs while you wait for the shock or the arrival of medical professionals.
Modern AEDs often provide CPR feedback, helping users improve compression quality. High-quality CPR has a significant impact on survival outcomes, especially when paired with timely defibrillation.
Manual Defibrillators: In Clinical Hands
Manual defibrillators are found in hospitals, ambulances, and by emergency responders. These allow trained professionals to:
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Assess ECG waveforms in real time
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Select the energy level for the shock
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Use pacing and synchronised cardioversion features
They're essential in controlled medical environments where tailored intervention is required.
Don’t Be Afraid to Use an AED
Public-use AEDs are safe, robust, and regulated. They will not deliver a shock unless one is needed. UK legislation and public health policy encourage their use, and in the event of an emergency, acting quickly is always better than doing nothing.
AEDs are designed to talk you through each step. Some units even come with CPR feedback, visual screens for noisy environments, or paediatric modes for use on children.
Choosing the Right Defibrillator for Your Needs
If you're considering installing an AED in your workplace, school, or community space, the main consideration is determining the right number of AED units and their optimal locations. The most important metric is how long it takes to retrieve a defibrillator and deliver a shock to the patient. Everything else — the size of the facility, accessibility of different areas, and how many people are typically present — ultimately feeds into minimising that time to treatment.
We often recommend a site survey to assess your building layout, access points, staffing levels, and risk zones. This helps determine both the ideal number of units and their precise locations.
Modern AEDs also offer varying levels of guidance, from basic voice prompts to comprehensive visual displays and real-time CPR feedback. The key is matching the device to your environment and the likely skill level of potential users.
Final Thought: A Defibrillator Could Save a Life
The next time you walk past an AED, take a moment to notice it. Knowing where one is could mean the difference between life and death.
At Defib Experts, we support organisations rolling out new defibrillator programmes and those managing existing fleets. Whether you need advice, site planning, product selection, or governance solutions, we’re here to help.
Every second counts. Every device matters. Every life is worth saving.
