BOSTON (CBS) — The finish line was a crime scene. More than 5,500 runners were stopped on the course and their safety was Dave McGillivray’s top concern.

“A police officer stopped me and said, ‘where are you going?’ and I said I’m going up to the finish line and he said no you’re not.”

READ MORE: UMass To Freeze In-State Tuition For Second Straight Year

McGillivray didn’t go home for two days as the investigation unraveled. Eventually, he completed the race.

He ran his 41st Boston Marathon 11 days after the race – a personal victory – but he knew something was wrong.

“I go out to run and I feel like I’m running at altitude for the first ten or fifteen minutes,” he said.

A cat scan revealed the problem – a severe blockage in the arteries around his heart and doctors couldn’t operate.

“I really thought for the first time in my life, that I only had a short period of time left,” he said.

The plan? better nutrition, medication, less stress and more sleep.

READ MORE: 4 Massachusetts Chocolate Shops Named Among The Country’s Best

He’s followed it religiously, losing 27 pounds and lowering his cholesterol by 70 points.

“I spent my whole life working really hard at being fit. I didn’t work at being healthy because I thought one meant the other and I was totally wrong,” he said.

Now fit and healthy, McGillivray’s taking on a new challenge – running the marathon for charity.

The father of five has an 8-year-old son. In honor of Martin Richard, he’s joined Team MR8.

“It makes the accomplishment that much more meaningful,” he said.

[display-posts category=”Boston Marathon” wrapper=”ul” posts_per_page=”4?”]

MORE NEWS: Lynn Tax Business Fined $136,000 For Prohibiting Employees And Customers From Wearing Masks