Nor will it stop him from taking on the New Zealand Ironman triathlon in March.

The defence force veteran said fellow athletes were regularly shocked to find out about the critical piece of metal keeping his heart ticking.

"I'm involved in veteran athletics here in Canberra and some people didn't know I had a pacemaker," he said.

"Whenever they'd find out they'd say, 'no way, you're way too young to have that' or 'you run way too fast to have that'."

Mr Purdon was diagnosed with sick sinus syndrome - a condition involving heart rhythm problems - in 1998, requiring him to check in with a cardiologist once a year.

In 2003 his health took a turn for the worse.

"I was feeling very tired, lethargic - generally run down. I was getting colds quite easily," he said.

"My cardiologist [at the time] told me I needed a pacemaker pretty much there and then. Whether it was three months, six months, 12 months, have a chat to your family and see what you want to do. I decided to have it done a few weeks later after a few more games of [Australian rules] football."

A day after his 31st birthday Mr Purdon had his pacemaker fitted.

It was a blow to the sports lover who was told he couldn't continue playing contact sport - until in 2005, when he was fitted with a special chest plate that enabled him one last season of AFL with the Australian Defence Force before retiring in 2006.

But the outlet football offered was soon replaced.

"In October 2006 I met my now wife, she was an endurance athlete so, to spend a little bit more time with her I started to run with her," he said.

"Seven or eight months later I did my first marathon.

"I watched my wife do an Ironman triathlon. Watching her achieve that and all the other people achieve a race that takes some people up to 17 hours to do, watching the sheer emotion, seeing people cry as they cross the line, I thought, 'I have to have a piece of that'.

"I started swimming when we got home - I suppose the rest is history."

Mr Purdon's sixth Ironman will put him in good stead for April's half marathon.

"I like half marathons. You can really really race those," he said.

"It's an hour and 22 minutes or something. You can really push your body.

"I've always been active. I love sport. I need the sporting outlet."