AEDs Explained: What to Do When Someone Goes Into Cardiac Arrest

What an AED Actually Does

An AED is a portable device that reads a person's heart rhythm and decides whether an electrical shock is appropriate. If the rhythm is shockable, it tells the rescuer when to deliver the shock. If it isn't, the device tells you not to shock.

You never have to diagnose the rhythm yourself. Your job is to turn the device on, place the pads correctly, and follow the prompts.

When to Use One

• The person is unresponsive
• They are not breathing normally, or only gasping
• Start CPR immediately and send someone for the nearest AED

How to Use an AED

• 1. Turn it on — open the lid or press the power button and listen to the prompts.
• 2. Expose the chest — remove or cut away clothing that prevents pad contact with bare, dry skin.
• 3. Apply the pads exactly as pictured on the pads themselves.
• 4. Stand clear while the AED analyzes the rhythm — no one touches the person.
• 5. Deliver a shock if instructed, after confirming everyone is clear.
• 6. Resume CPR immediately, continuing about two minutes before the AED reanalyzes.

Can an AED Hurt Someone?

A common fear is shocking someone who doesn't need it. Modern AEDs analyze the rhythm first and will not deliver a shock simply because a button was pressed.

The device — not the rescuer — makes that decision.

CPR and AEDs Work Together

An AED doesn't replace CPR. Compressions keep oxygenated blood moving while the AED evaluates the rhythm and, when appropriate, delivers a shock. Early high-quality CPR plus prompt defibrillation are the interventions most associated with survival in adult cardiac arrest.

If you're alone: call 911, put the phone on speaker, start CPR, and use an AED as soon as one is available. With more people present, split the roles — one calls, one compresses, one retrieves the AED.