If an off-duty doctor didn't know a nearby school had a defibrillator, Steven Simpson thinks he might not have made it through a recent heart attack.

Mr Simpson had just made son Liam a coffee on June 28 when he went into cardiac arrest, leaving his son to call triple-zero and start delivering CPR.

But while he waited for an ambulance, the GoodSAM app notified emergency doctor Rhys Ross-Browne of the incident, and he attended to take over care.

"Apparently there was a knock on the door, a guy turned up and said, 'I'm a local doctor, I got a message there was a cardiac arrest. I'm here to help you'," Mr Simpson told AAP.

"That amazed us. I'd never heard of (the app)."

The free app alerts registered community members to nearby incidents in the hope it cuts the gap between triple-zero calls and the start of CPR for victims of cardiac arrest.

The NSW public access defibrillator registry has been incorporated into the app, in what should be a huge boost to a victim's chance of survival.

Mr Simpson knew it was what saved him - Dr Ross-Browne shocked him twice before the ambulance arrived before paramedics had to give him another three hits.

Dr Ross-Brown didn't have the benefit of the app guiding him to a defibrillator, but happened to know a nearby school had one on hand.

"Defibrillators are all out in the community, a lot of businesses have them, but nobody else knows they've got them," Mr Simpson said.

"It would be massive if every one of them registered their location so when something like this happens and they've got volunteers coming to help you, they also get told where the nearest defibs are ... it would save so many more lives."

More than 4300 defibrillators are registered with the app.

GoodSAM volunteers have helped save 30 patients since the app launched in November, with 12 of them benefiting from a defibrillator shock before an ambulance arrived.

Health Minister Ryan Park said volunteers being guided to the devices could hugely improve the cardiac arrest survival rate.

"It's all well and good to have defibrillators around the community, but if people don't know their location, they're going to be of little help in a life and death situation," he said.

"I encourage everyone who has an AED to register it online with NSW Ambulance so GoodSAM responders can see it in the app."