If you find someone collapsed, make sure it's safe to approach, check if they respond by gently shaking their shoulders and asking them loudly if they are ok.

If they don't respond, shout for help and open their airway. Look, listen and feel for up to 10 seconds for normal breathing (ignore occasional, irregular gasps - these are common in the early stages of cardiac arrest).

If they are not breathing, ask a helper to call 999 or 112 for an ambulance while you start chest compressions. Ask a helper to find and bring a defibrillator, if available.

• Ask your helper to put the phone on speaker and hold it out towards you.
• If you are on your own, use the hands-free speaker on a phone so you can start CPR while speaking to ambulance control.
• Do not leave the casualty to look for a defibrillator yourself. The ambulance will bring one.

Start CPR. Kneel by the casualty and put the heel of your hand on the middle of their chest. Correct hand placement for CPR on a person with breasts may mean that your hands may touch some of the breast. This is okay.

Put your other hand on top of the first and interlock your fingers. Keep your arms straight and lean over the casualty. Press down hard, to a depth of about 5-6cm before releasing the pressure, allowing the chest to come back up.

Push at a rate of 100 to 120 per minute. Listen to instructions from the ambulance controller, who will tell you what to do and help you to push at the right speed.

Continue to perform CPR until:

• Emergency help arrives and takes over.
• The person starts showing signs of life and starts to breathe normally.
• You are too exhausted to continue (if there is a helper, you can change over every one-to-two minutes, with minimal interruptions to chest compressions).
• A defibrillator is ready to be used.

When the helper returns with a defibrillator, ask for it to be switched on and to take the pads out, while you continue CPR.

They should remove or cut through clothing to get to the casualty's bare chest. This includes removing bras or binding if the person is wearing one. The helper needs to cut through the bra or binder up the middle or side of the clothing.

The AED should come with safety scissors. They also need to wipe away any sweat. The defibrillator will give you voice prompts on what to do.

• If no scissors are available and you cannot expose the skin, continue performing chest compressions until emergency services arrive.

The helper should attach the pads to the casualty’s chest, by removing the backing paper. Apply the pads in the positions shown.

• The first pad should be on the upper right side below the collar bone.
• The second pad should be on the casualty’s left side below the armpit.
• If the person has larger breasts, moving the left breast back towards the centre of the chest will allow correct placement of the AED pad.

The defibrillator will analyse the heart’s rhythm. Stop CPR and make sure no one is touching the casualty. It will then give a series of visual and verbal prompts that should be followed.

• If the defibrillator tells you that a shock is needed, tell people to stand back. The defibrillator will tell you when to press the shock button. After the shock has been given the defibrillator will tell you to continue CPR for two minutes before it re-analyses.
• If the defibrillator tells you that no shock is needed continue CPR for two minutes before the defibrillator re-analyses.

If the casualty shows signs of becoming responsive, such as coughing, opening eyes or speaking, and starts to breathe normally, put them in the recovery position Leave the defibrillator attached. Monitor their level of response and prepare to give CPR again if necessary.