The 15-year-old was in the grip of cardiac arrest – her heart had stopped and she had no pulse – when her mother rushed her to the emergency ward.

Doctors say it was Kelly Madigan's quick actions and a swift response from the hospital's emergency team that miraculously saved her daughter's life and allowed her to make a full recovery.

Leanne was in the car with her mother when she suddenly began to writhe in her seat, her eyes rolled back in her head and she started to breathe heavily the morning of August 15.

Ms Madigan, of Cook, wasted no time and headed for the northside hospital's emergency department.

Not long before she pulled into the car park, Leanne stopped breathing altogether.

Dr David Caldicott, an emergency medicine specialist, was among staff who had just finished their morning handover when an alarm sent them running outside.

A paramedic who was nearby had already started to perform CPR.

"She clearly wasn't breathing and she clearly didn't have a pulse, which is very unusual in someone her age," Dr Caldicott said.

As emergency staff tried to move Leanne onto a trolley they noticed a large "zipper" scar on her chest from a major heart operation she had as a child.

"That was a real sign that this could be something more than an overdose or something we see from day to day."

"It was very clear that she was in a rhythm called ventricular fibrillation, which is one that's very quickly not compatible with life."

Up to 20 doctors, nurses and paramedics continued CPR and shocked Leanne's chest with a defibrillator in a desperate attempt to re-start her heart.

"Her rhythm came back but she wasn't breathing so we took her into the resuscitation suite and she needed additional shocks after that.

"She had quite an unstable cardiac rhythm."

Once Leanne started to breathe again, doctors were able to stabilise her until a rescue helicopter arrived.

She was flown to Sydney's Westmead Children's Hospital, where she remained in intensive care for a week.

Doctors believe scar tissue from her previous surgery caused the cardiac arrest and fitted Leanne with an implantable cardiac defibrillator to regulate her heart rhythms.

Dr Caldicott said while Leanne had not suffered a loss of brain function which would have rendered her clinically dead, "there were certainly no signs of life."

He said the outcome could have been very different were it not for Ms Madigan's rapid response.

"Her getting Leanne here saved her life, there's no doubt in my mind.

"Had there have been any more delay, Leanne would at the very best have had a greatly diminished outcome."

Dr Caldicott said it was "extraordinarily rare" for a patient so young to suffer cardiac arrest and survive without lasting neurological damage.

"The survival of an out of hospital paediatric cardiac arrest is around 5 per cent.

"So between 90 and 95 per cent of people in her situation would have died.

"You could anticipate that significant number of those would have some sort of deficit, but there's absolutely none here, she's as sharp as a tack."

For the hospital's emergency staff, Leanne's miracle recovery was justification for their hard work and rigorous training.

"I could not anticipate how a resuscitation could have worked better in these circumstances, it was extraordinary to see all the stops being pulled out to resuscitate this little girl," Dr Caldicott said.

"I'm still moved by it today."

Leanne, who is in year 9 at Canberra High School, has no memory of the extraordinary ordeal.

But she gained some insight when was reunited with hospital staff who treated her this week.

"It's a pleasure to meet everyone and be able to thank all who supported and helped me through this journey," she said.

"I feel privileged. I feel happy I survived but I'm definitely happy I had such a good team behind all of what happened.

She was presented with a tongue-in-cheek framed certificate, celebrating her election as patron of "The Calvary Car Park Club".

Dr Caldicott said the incident was a "salient lesson" that CPR could save lives.

"People who don't know how to do it should go and learn because it's not just your grandpa you might perform it on, it may be someone a lot younger with a lot more still to offer."