Cardiac Emergencies 101: What Is An AED & How Does It Work?

You have probably watched several high-stakes medical drama TV shows: Grey’s Anatomy, House M.D., Scrubs—you name it. In first-aid scenarios, doctors would grab two external paddles, place them on the patient’s chest and yell ‘Clear!’ to jolt them back to life.

These scenes keep viewers on the edge of their seats. Will they get the heart beating again?

The devices at play are called defibrillators, commonly known as AEDs (Automated External Defibrillators). Although the process looks less theatrical in real life, their roles in emergency response and first aid training significantly increase the chances of survival during a sudden cardiac arrest.

Moreover, they aren’t just limited to hospital settings and medical practitioners. AEDs are user-friendly, making them accessible to a broader audience—paramedics and bystanders without a medical background or training.

But what is an AED and what is it used for? How does it work? In this blog post, we’ll discuss the inner workings of AEDs, their benefits, a step-by-step tutorial on how to use them in an emergency and first aid courses you can take. Read on to learn more!

Defining Defibrillators: What Is An AED?

An automated external defibrillator, also referred to as AED, is a portable device used to help people suffering from abnormal heart rhythms—ventricular fibrillation and ventricular tachycardia—during a sudden cardiac arrest. Rapid intervention is crucial, as both abnormal rhythms can be fatal if not dealt with within a few minutes of onset.

Equipped with a sensor that analyses the heart’s electrical activity, it sends a controlled electric shock to restore its normal rhythm. It has two main types:

  • Professional use AEDs: These AEDs are typically used by first responders including paramedics and emergency medical technicians (EMTs). They undergo specialised training and first aid courses like a CPR AED course and Basic Cardiac Life Support (BCLS) + AED to handle these devices.
  • Public access AEDs: AEDs designated for public use are found in community centres, schools, airports, hospitals, government offices and other public spaces.

They can also be classified into two types, mainly:

  • Fully automated defibrillators analyse the heart’s rhythm and automatically deliver a shock without user intervention. Since they are designed for individuals with little to no medical training, they usually have simpler interfaces and clear prompts.
  • Semi-automated external defibrillators also analyse the heart’s rhythm. However, once the device detects an abnormal rhythm, it requires the user to initiate a defibrillation shock by pressing a button. The user interface may also require additional steps that need to be followed by the operator.

How Does an Automated External Defibrillation (AED) Work?

An automated external defibrillation (AED) uses texts, lights and voice prompts to instruct the user on the steps they should take. AED machines also consist of several components, including:

Electrode Pads

Image source: Cardinal Health

The AED comes with adhesive electrode pads that need to be applied to the patient’s bare chest. These pads mainly serve as sensors that monitor and detect the heart’s electrical activity. If the AED’s processor deems a shock necessary, the electric shock travels between the pads and passes through the patient’s heart.


The capacitor in an AED is an energy storage component that comes in different capacities or sizes. Once it detects a shockable rhythm and the AED’s processor determines that a shock is needed, the capacitor rapidly charges to a specific energy level.


AEDs are powered by batteries—usually lithium batteries—to provide the necessary energy to deliver a life-saving shock. They also power the device’s internal components, including the charging system and the processor.


The processor is the brain of the AED. It analyses the patient’s heart rhythm through the electrode pads and determines whether a shock is needed. Additionally, it controls the strength and timing of the electric shock.

Other components also include a shock button for semi-automatic AEDs, display screens, control panels and more.

Benefits of AEDs: Why Should You Get One?

According to the Singapore Heart Foundation, more than 3,000 people suffer from sudden cardiac arrest each year. Studies have shown that more than 80% of these reported incidents happened in public and residential settings.

This is why making a cardiac emergency plan that includes an automatic external defibrillator could make all the difference. To delve deeper into this matter, let’s discuss the benefits of having an AED at home or in public:

Increases The Chances of Survival

The simplest and biggest advantage of having an AED is it saves lives. As reported by Steroplast Healthcare, the patient has a 50-70% chance of survival if defibrillation occurs within five minutes of a cardiac arrest.

For every minute that passes without CPR or AED, the likelihood of survival diminishes by 10%.

The prompt use of an AED, especially within the crucial initial minutes, plays a significant role in restoring a normal heart rhythm and keeping the person alive until ambulance services arrive. This, in turn, can drastically improve workplace safety and first aid.

They Are Easy To Use

Given its lengthy and somewhat intimidating name, it’s easy to assume that an AED device is complicated to operate. But contrary to popular belief, AEDs are easy to use, even for individuals with minimal or no medical training.

AEDs come with straightforward, step-by-step voice and visual prompts. They will guide the user through every critical step of the resuscitation process, such as CPR, shock delivery and proper electrode placement.

The device is also equipped with automated heart rhythm analysis. You won’t have to get involved in a complex decision-making process because the device itself will determine whether a shock is needed or not.

Most importantly, a lot of first aid courses or training programs allow users to practise using the device in a simulated environment. With this kind of hands-on training, users will feel more confident when using the device in an emergency.

Protection from Stressful Work Environments

As of writing, there is no national requirement that obliges employers to install wall-mounted AEDs in the workplace. However, anyone can suffer from a sudden cardiac arrest even if they’re just sitting in their cubicles for eight hours straight.

This is even truer for workers who handle strenuous tasks. This includes being in extreme temperatures, operating heavy machinery for extended hours, working at heights or any activity that pushes the human body beyond its limits.

That’s why implementing an AED program for employees at higher risk should be included in an emergency response plan. Employers should provide several accessible defibrillators throughout a worksite and train employees on their locations and proper usage with CPR + AED courses.

How To Use an AED: A Step-By-Step Guide

Using automated external defibrillation (AED) comes with a series of steps called CALL-PUSH-SHOCK to ensure an effective and safe first aid process. Take a closer look at this step-by-step guide:

Step 1: Assess The Situation and CALL An Ambulance

Image by on Freepik

To make sure that there are no potential hazards or dangers around, perform a quick survey of the scene. There shouldn’t be a metallic or wet surface and flammable gas.

Next, assess the person’s responsiveness. If the patient is not breathing and is unresponsive, call ambulance services before starting the AED process.

Step 2: PUSH And Perform CPR

The second step involves performing cardiopulmonary resuscitation (CPR) through chest compressions. Apply firm and rapid pressure to the middle of the chest while someone retrieves the AED, helping circulate blood containing oxygen to the vital organs. This will improve the chances that the heart will respond to the subsequent shock.

Step 3: SHOCK Using An AED

Image source: National Heart, Lung and Blood Institute

Immediately proceed to defibrillation. Here are the steps you should follow when using an AED:

  1. Power on the AED. Press the power button to initiate voice and/or visual prompts.
  2. Expose the patient’s chest. Before applying the AED electrode pads, remove any clothing covering the person’s chest. Ensure that the chest is dry, clean and bare.
  3. Apply the AED electrodes. Follow the graphics on the pads to properly attach the electrode pads to the designated areas on the bare chest. One pad is usually placed on the lower left side below the left nipple, while the other is placed on the upper right chest under the collarbone.
  4. Analyse heart rhythm. Once you have properly attached the pads, the defibrillator will give a quick prompt and determine whether a shock is needed.
  5. If needed, deliver a shock. If the AED device determines that the patient is suffering from a sudden cardiac arrest and a shock is necessary, shout ‘Stay Clear!’ to make sure that no one touches the patient.This will depend on whether the AED is a fully automated or semi-automatic model.
    1. Fully automatic AED: In the event of a necessary shock, it will count down and automatically deliver the shock without requiring you to press a button.
    2. Semi-automatic AED: When a shock is needed, it will prompt you to push a button to administer a shock. The button is typically flashing and easily identifiable during an emergency, but extra caution is required to avoid pressing the power button.
  6. Perform CPR & re-analyse. According to the American Heart Association’s (AHA) guidelines, the rescuer should perform two minutes of CPR between intervals of heart rhythm analysis by the AED. follow the AED’s instructions for the rate and depth of chest compressions.
  7. Continue until help arrives. Continue listening to the AED’s prompts until the person shows signs of life or professional medical help arrives.

Remember, the key to successful defibrillation and increasing the chances of survival is to act quickly and accordingly. Stay calm, accurately follow the prompts and take a CPR + AED course to enhance your confidence in an emergency like this.

Most importantly, AEDs are not toys. Just because these devices can be used by almost anyone doesn’t mean they shouldn’t be handled with utmost care. You should never use AEDs on people who are still conscious or responsive since it can cause more harm than good.

Where Should You Keep Your Automated External Defibrillation (AED)?

Keep in mind that the placement of your AED is crucial, especially when the device is needed in emergencies. Here are the important points to take into consideration when it comes to keeping AEDs:

  • Ensure the AED is easily accessible and visible to all individuals, with elevated wall signs for clear sight lines. It shouldn’t be higher than 48 inches, and the unobstructed side reach should be a maximum of 54 inches.
  • Place them near landmarks within the building. This way, you can instruct someone to get the AED ‘next to the front desk’ or ‘near the bathroom door’ while you assess the situation at hand.
  • Avoid placing the AED in a locked room. If you plan to use lockable cabinets for AEDs, make sure to install alarms. This will help deter theft and alert bystanders. Just make sure that you strike the right balance between security and accessibility.
  • Position the AED near a phone for use during emergency calls. You can find an AED cabinet that automatically notifies paramedics when opened.
  • For offices, schools and churches where specific areas may be restricted during specific hours, ensure a clear path to the AED. You should also consider getting an additional AED for outdoor activities.

It is also recommended that certain additional items should be placed with an AED to ensure maximum effectiveness. These may include:

  • CPR mask, face shield and disposable gloves. This is used to provide a barrier between the patient and the rescuer, minimising the risk of infection.
  • Razor. If the patient has excessive chest hair, a razor can be used to quickly remove hair for the proper adhesion of the electrode pads.
  • Scissors. Blunt scissors can be used to cut away clothing or other obstacles that may interfere with electrode pad placement.
  • Towel or wipes. This is handy for cleaning the patient’s chest if it is wet or sweaty.

You may consult with our industrial paramedic services for site assessment of your workplace and other public settings.

How Should You Properly Maintain an Automated External Defibrillation (AED)?

Imagine this: you’re talking to a coworker on a usual Monday morning. In a split second, he collapses right in front of you. You spring into action and quickly assess your environment, thanks to the First Aid + AED course you recently completed.

You recall the AED mounted in the hallway and instruct someone to retrieve it for you. But when you open the case and try to turn the device on, nothing happens. The batteries are dead, and with each second that passes, the chance of them surviving passes too.

AEDs are lifesaving, but their presence in emergencies can be futile if not properly maintained. To make sure you truly save a life, follow and perform these maintenance tips regularly:

  • Perform regular inspections. Conduct a visual inspection of the device and check for any physical damage, signs of wear or cracks. Make sure the buttons, indicators and display screen are functional.
  • Inspect electrode pads and battery expiry. Always verify the expiration dates of electrode pads and batteries. Read the manufacturer’s guide and replace them accordingly.
  • Confirm the AED has a sufficient power source. Keep it plugged into the wall when not in use to maintain the primary battery’s power.
  • Monitor indicator lights. Pay attention to the indicator lights on the AED. For instance, a green light indicates readiness, while red indicates a problem.

We highly recommend keeping a checklist during each inspection so nothing goes overlooked. You can find an AED maintenance checklist online or make your own using the user manual.

Learn AED Usage The Right Way: Where To Get CPR and AED Training

Many AED devices are built specifically for lay people. It doesn’t matter if you have undergone basic first-aid training or consumed information about cardiac arrests; if you know how to follow instructions and read, you can save a life.

They have voice and/or visual prompts, indicator lights, easy-to-use buttons and other features to help bystanders act swiftly in critical moments.

Their design recognises that in high-stress situations, simplicity is key. Anyone, regardless of their medical background, can be the lifeline someone desperately needs.

However, while AEDs are designed to be user-friendly, understanding how to operate them within the context of an emergency response is important. Taking CPR and AED training programs will help you recognise the signs of cardiac arrest, and practise first aid skills in a controlled environment and act decisively when faced with a crisis.

Join Medlink in our commitment to creating a prepared and safe community. Our first aid courses include Basic Cardiac Life Support (BCLS) + AED, CPR + AED and more to empower you in making a difference—one life at a time.

Let’s go beyond the basics. Get in touch with us today!


What is an AED?

An AED, or Automated External Defibrillator, is a device that delivers an electric shock to the heart when a person suffers from a sudden cardiac arrest. The shock can restore the heart’s normal rhythm and save someone’s life.

When should an AED be used?

An AED should be used when someone is experiencing cardiac arrest. Make sure the person is not breathing before starting the AED process.

What is the AED 3-minute rule?

The AED 3-minute rule suggests that the best chance for survival when using an AED should occur within the first three minutes. The sooner the defibrillation takes place, the higher the chances of restoring the heart’s normal rhythm.

About Medlink Healthcare Group

Committed to providing a comprehensive healthcare ecosystem, Medlink Healthcare Group delivers top-notch ambulance services, first-aid courses and industrial paramedics. We aim to empower individuals, businesses and communities to effectively respond in times of medical emergencies, right when it matters the most.

Our first aid courses cover a wide range of topics, including a CPR + AED course, BCLS course, occupational first aid course, and a standard first aid course in Singapore—both accredited by SRFAC. Whether you’re an individual looking to acquire life-saving skills or a business investing in workplace safety and health training, we have the right course for you.

Alongside training programs, our private ambulance services are led by highly trained paramedics and equipped with cutting-edge medical technology. Every second counts; we are always ready to provide prompt and expert care when you need it most. 

Our industrial paramedics solutions can also meet the unique needs of your workplace, from on-call doctors to screening exercises and specialised clinics. We ensure that you have access to the right medical services to keep employees safe and sound, no matter where they are. 

Your journey to safety starts with us. Contact us today and prepare to respond in any emergency.

This blog post is for informational purposes only and is not intended as a substitute for a comprehensive first-aid course provided by certified professionals. Readers are strongly encouraged to acquire a first aid education to receive the appropriate training and certification.

We do not assume responsibility for any actions taken based on the information provided in this article. Always consult with certified first aid professionals and seek hands-on training to ensure you are well-prepared to handle emergency situations competently.

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