John Quinn, a retired newspaper editor, likes to wear the teal cotton T-shirt he got from the 2012 Broad Street Run, a 10-mile race in Philadelphia. It was his first 10-mile event, and he’d come a long way to get to that 2012 starting line: losing more than 60 pounds and going from calling himself “John 316,” a reference to his previous weight, to being a dedicated runner.

“Getting into shape, it’s not glamorous,” he said. “It’s hard. You can’t fake it.”

But less than four years later, in 2015, Mr. Quinn, now 64, had a heart attack from a complete, sudden blockage of his right coronary artery. That led to part of his heart dying and a tear in the muscle bridge that separates the left and right ventricles.

If that all sounds bad, it was. Repairing that bridge is a delicate procedure, and about 50 percent of patients die within 30 days after the operation, according to Dr. Matthew L. Williams, assistant professor of cardiac surgery at Presbyterian Medical Center of Philadelphia and Mr. Quinn’s surgeon.

Mr. Quinn spent 53 days in the hospital. He pulled through it, and then had a follow-up surgery to implant a pacemaker.