Everything you wanted to know about defibs...

Fraser: If someone is in cardiac arrest, it means their heart has stopped beating in its usual rhythm, and it has stopped pumping blood around the body. A defibrillator works by giving an electric shock to the person’s heart to kick-start it back into normal rhythm.

A lot of defibs you see in public places are in cabinets which protect them from cold weather and mean they can be accessed 24/7 in an emergency. If you ever need to get into one of these boxes and it’s locked, tell the ambulance service operator where you are and they will give you the code to unlock it.

There are lots of different makes of defibrillator, but they all essentially work the same way. All you need to do is press the ‘on’ switch and follow its instructions. Some will analyse the heartbeat and provide a shock automatically, others will tell you to press a button to deliver the shock. The machine will only deliver a shock if it would be helpful. If not, it will say "no shock required" and you can continue with CPR.

A defibrillator will only deliver a shock if one is needed. It simply will not shock someone whose heart is working properly, so you can never hurt someone with one.

Cardiac arrest is one of those situations where you really need to act as quickly as possible. Without action, the person could die within minutes. To be most effective, you need to start CPR immediately and use a defibrillator as quickly as possible. So remember – phone 999, start CPR, ask someone to get a defib if one is available, and keep going until the ambulance arrives.