The TV host's grandfather had died of heart attack at age 36, the same age at which he then suffered his second attack.
"I just started beating my chest, I could feel my heart in my head. I felt tingles down my arms."
It was then, two years ago now, that Tristan was told he'd had a second heart attack and was diagnosed with myopericarditis, which is inflammation of the heart muscle and the pericardium.
"Your arteries are supposed to sit on top of your heart, it turns out mine go through my heart."
Despite living with the fear he could suffer another attack at anytime, only managing the disease by staying on top of his health, his main concern is his children.
Tristan and wife Tahyna Tozzi of Blue Water High fame share four-year-old daughter Echo and one-year-old son Oisin and have a third child due in April.
"There will always be that fear. I couldn't think of anything else that would be more scary than not seeing my kids grow up."
"Three strikes and you're out."
The couple are on the fence about whether they will have anymore children.
"I could go another, five is the magic number I think," Tristan said.
But Tahyna added: ”Tristan would have a whole football team if he could – but he's not the one carrying them!"
Tahyna and Tristan were introduced by mutual friends in 2011 at a Thai restaurant in LA - and it turns out the friends were secretly setting them up!
They dated for five years, splitting their time between Ireland and LA, before getting married in 2014 in Sydney's Cronulla.