Talk about an emotional moment!

Over a year ago, "The Biggest Loser" alum Bob Harper had what's called a widowmaker's heart attack (i.e. a heart attack caused by a blockage at the main artery at the front of the heart). As Bob told us, it was not only a terrifying moment in his life, but one that caused him to change everything.

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"I had to change everything in the past year," he says. "My diet and my exercise. My whole life."

But he adds, "I think the hardest part for me is the emotional aspect — the fact that I had to redefine myself."

Slowly, Bob did get back to working out. But one thing the celebrity personal trainer didn't do? What he does best -- teach a class.

Until just before this episode!

Bob returned to his gym, Brick New York -- the gym where, though he says he can’t remember it, he suffered his heart attack -- and taught (our studio audience!) a circuit class that included jumping jacks, squats and cycling (and, you know, a whole lot of sweat).

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The best part? He brought us along to watch!

"It couldn't have been better,” he tells us.

And we couldn't be happier!

Watch him in action, teaching the class, in the video above!