The volunteer firefighter in his late 60s (who the Tribune has not named out of respect for his privacy) was about to start his shift helping manage the event's car parking when he began to feel unwell.

He fell to the ground and went into cardiac arrest. Another RFS member, who had been walking through the car park with him, raised the alarm by calling 000.

"NSW Ambulance was initially called to a man who was suffering from chest pain and feeling unwell," NSW Ambulance Inspector Ben Hutchinson said.

RFS and St John Ambulance first aiders rushed to help and began CPR.

They carried out CPR for a staggering 17 minutes.

During that time, another volunteer firefighter grabbed a defibrillator from an RFS vehicle and used it until the paramedics arrived.

On scene, paramedics delivered three shocks via an AED. They kept performing CPR until the firefighter began to breathe unaided again.

"We transported the man to Canberra Hospital in a critical condition; however, his condition improved," Inspector Hutchinson said.

It was the RFS members' quick-thinking that saved the firefighter's life, Inspector Hutchinson said.

NSW Ambulance has commended the work of those who immediately gave CPR to the man.

"This early and effective CPR goes a long way in ensuring a patient has the best possible chance of survival and making a full recovery," Inspector Hutchinson said.

Restart a Heart Day was on October 16, highlighting the importance of community members knowing CPR.

A cardiac arrest is when the heart stops, Inspector Hutchinson explained.

"Three simple messages for anyone who goes into cardiac arrest. For those around them: Call. Push. Shock."

Compressions should be given to a depth of a third of the chest, he said.

Signs include no pulse, absent or gasping breath, unconsciousness and colour change (blue or purple).

The symptoms can include chest pain but not always, clammy skin, shortness of breath, dizziness, nausea and vomiting.

The RFS provides first aid and advanced resuscitation training and the members who provided assistance on the day were qualified, NSW RFS operational officer - Southern Tablelands Zone, Lachlan Gilchrist said.

He said the RFS was "enormously grateful" that the firefighter was okay and thankful to the "wonderful volunteers who did an extraordinary job".

"After speaking to those who were involved on the weekend, they would be among the first to dismiss the suggestion that what they did was heroic. But 72 hours after a cardiac arrest, he was back home recovering with his family," Mr Gilchrist said.