Harnett will be taking part in his 15th Becel Heart & Stroke Ride for Heart, the largest one-day charity cycling event in Canada.
Last year the Toronto ride raised $4.2 million for the Heart and Stroke Foundation. The goal this year is $5 million.
"I had a grandfather that passed away at a young age as a result of a heart attack, so it's something that's close to my heart, pardon the pun," said Harnett.
"But at the same time (it's) a great opportunity for me to be out promoting a sport that's so near and dear to my heart."
Former Olympic champion rower Marnie McBean is another celebrity spokesperson for the charity ride.
The men on her father's side of the family have a genetic predisposition to heart issues. And her brother had a narrow escape.
"My brother one day came home, he was skiing and he just thought he was getting older and he wasn't recovering well," McBean recalled. "His wife knew all the signs and symptoms and said 'You're being an idiot,' got him to hospital. That was in Whistler and he had a stent put in the next day that possibly saved his life.
"So it's one of those things that the more people know about, how to identify heart distress, the better we are at managing it and dealing with it. Sometimes it's not our lifestyle, sometimes it's just our genetic code."
Harnett was the ride leader on the race's 10th anniversary. Now he is taking part in its 25th year.
"It's just exciting to ride the Don Valley Parkway with over 13,000 of my closest friends," said Harnett.
The DVP and Gardiner Expressway, two major arteries in the city, are closed for the charity ride, which comes in three distances: 25, 50 and 75 kilometres.
Funds raised will go towards research, health promotion and advocacy. The charity ride has raised more than $40 million for research since it started.
According to the Heart and Stroke Foundation, heart disease and stroke take one in three Canadians before their time and it is the No. 1 killer of women.
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