When someone goes into cardiac arrest, the heart is either in a useless, abnormal rhythm, or without rhythm. 

Automated External Defibrillators (AEDs) are an effective way for any person to try to help correct an abnormal rhythm.

While there are no guarantees, it could potentially save a life.

Here are three things you should know:

1. When someone goes down, minutes mean everything

Step one: call 911.

Step two: send anyone nearby for an AED.​ 

According to the Heart and Stroke Foundation of Canada, someone using an AED has up to a 75 per cent chance of saving a life, if the machine is used immediately. After more than 12 minutes, the cardiac victim’s chance of survival is less than five per cent. 

2. The machine determines whether to shock, not you

If you just aren't sure whether an unresponsive person is in cardiac arrest, turn the machine on and follow instructions.

Once connected, it will read the electrical activity in the person’s body. If it needs to shock, the machine will tell you to stand clear and hit the button.

3. Don't worry about a lawsuit when using an AED 

Every province has legislation protecting from legal reprisal any person doing his or her best to save a life, even if something goes wrong or the patient doesn't survive.