Jamaican athlete Kemoy Campbell was told by doctors he had "died" after collapsing on the track during February's Millrose Games in New York.
The 28-year-old was acting as pacemaker in the men's 3,000m when he fell into the infield and had to be given medical attention by the side of the track.
"I have no recollection of it," he told BBC World Service.
"The doctors said my heart stopped and I basically died. It was a scary moment for me."
Campbell spent 17 days in hospital and had a procedure to implant an internal defibrillator (ICD). He added that despite "numerous tests" doctors were unable to deduce the cause of the heart failure.
"When I woke up it was Monday morning (two days after the race) and I was in hospital," he added.
"I didn't know where I was and how I got there. It was scary to know I missed almost a whole two days and couldn't recall what happened."
A donation page has been set up by his girlfriend, and sponsors Reebok have given him $50,000 (£38,000, Sh5 million) to help with the "hefty" medical bill he expects to receive, as he had no medical insurance.
Regarding his future, he added: "In my mind I should be back on the track. Doctors say I should take some time off then do some tests, then maybe I can start slowly and build back up.
"If I can't, it'll be the end of my career."