The 52-year-old was the only one working in Casterton, Victoria, on May 30 when he was struck by sudden chest pain.
Recognising the symptoms, he rushed to the ambulance and hooked himself up to the ECG.
“I was just warming up to do a workout, and just got the sudden onset of crushing chest pain and tingles down both arms, so I quickly rushed in, grabbed the heart monitor from the ambulance, put myself on it and thought, uh oh, that's not right,” he told 3AW Radio.
He miraculously managed to drive himself to the local hospital where other paramedics took over.
David was then flown to Geelong and had a stent put in his artery.
“He [the doctor] said, ‘it's amazing you're alive’ because the clot was in one of my large coronary arteries,” he said.
“I went to the doctor yesterday, and he said I’m lucky to be alive because I was so quick to get on to it, because I was able to self-diagnose.”