If someone collapsed beside you, what would you do?

Check their pulse? Try and remember mouth to mouth? Or would you just wait for the ambulance to arrive, for someone who knows what they're doing?

In Australia, if you suffer a sudden cardiac arrest—an electrical malfunction of the heart, not a heart attack—there’s only a 9 -10 per cent chance that you’ll survive.

It all comes down to a pretty basic life skill: CPR.

In cities like Seattle, patients have around a 62 per cent chance of surviving - because CPR is far more widely taught. Around 75 per cent of their population know exactly what to do when someone suffers a sudden cardiac arrest (SCA).

Professor of Emergency Medicine Paul Middleton, the Chair of Take Heart Australia, says Seattle is setting the right example.

They make a joke in Seattle - if you fall asleep on a park bench in the summer, someone will probably resuscitate you.

In Australia, around 30,000 people die after having a sudden cardiac arrest each year. It’s one of our biggest killers.

Take Heart Australia aims to lift the number of Australians who know CPR. Yesterday, Take Heart taught more than 2000 people how to perform CPR at Allianz stadium - but there's still a long way to go.

Not many people who suffer SCA make it - but 17-year-old Leanne Madigan was one of them.

Last year, Leanne’s mum Kelly was driving her to school in Canberra. It was just like any other day.

But after Leanne started moving around in her seat, and eventually stopped breathing, Kelly rushed her daughter to a nearby hospital.

“I feel there was definitely someone watching over us that day,” Kelly told Hack, “We got all the green lights, I didn’t need to speed or anything, everything just sort of fell into place.”

When they arrived at the hospital a few minutes later, Leanne was resuscitated immediately - by doctors who had just completed CPR training.

Kelly says timing was everything that day - 30 seconds later, and Leanne would have been at school, where bystanders might not have known how to perform CPR to save her life.

“It could have been a very different situation.”

What is Sudden Cardiac Arrest?

Professor Christopher Semsarian from Royal Prince Alfred Hospital says SCA is an “electrical malfunction” of the heart. It’s got nothing to do with age, weight, diet or blocked arteries.

Symptoms that could lead to SCA often go undetected or misdiagnosed. “Sadly, every week in the clinic I see parents who have lost a son or a daughter, and they can’t believe a young person can have heart disease,” Professor Semsarian says.

Symptoms like dizziness, unusual tiredness or breathlessness after exercise can be easily missed.

For Sydney mum Jill Masurkun, an undetected heart condition led to the death of her 16-year-old son, James.

In August 2010, James went to bed one day after playing football. During the night, James suffered a sudden cardiac arrest - and he never woke up.

Skip Instagram Post FireFox NVDA users - To access the following content, press 'M' to enter the iFrame. A photo posted by Take Heart Australia (@takeheartaust) on Nov 2, 2015 at 12:54am PST

“I think I was pretty shocked, I suppose, at my lack of knowledge,” Jill told Hack, “But there was really no means of protecting my son from this event, because I was certainly not armed with the knowledge that I have now.”

Jill says the shock of losing someone so young is overwhelming.

One minute you do have a perfectly fit, healthy teenager, only to lose them suddenly.

But if more testing and screening was in place in Australia to detect heart conditions, teenagers like James could be saved.

And it could be as simple as an annual form - prompting young people to be wary of potential symptoms, like breathlessness or dizziness.

James went to a sports high school, where students did have to fill out some medical forms - but there weren’t prompts about SCA. Jill says adding a checklist with SCA warning signs could easily save lives.

“They fill in these forms anyway, why not make them meaningful?”

Legislation changes needed

To lower the amount of SCA deaths in Australia, Professor Christopher Semsarian says a change in legislation is crucial.

Professor Semsarian says the first step is ensuring more Australians learn CPR, and having more defibrillators—those machines that essentially restart the heart—available publicly.

We learn how to swim, we learn how to use a fire extinguisher, why shouldn’t we learn how to use CPR and a defibrillator as well?

“We need to actually change legislation. Every shopping centre, every school every workplace should have a defibrillator, and everyone should learn CPR.”