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(CNN) -- In medical school, Gerald Karpman was taught that when it comes to matters of the heart, what's done is done.

"If you survived the heart attack, you survived at the level that you were going to be," he recalls. "Whatever damage was done was permanent."

That thinking has prevailed until very recently, when studies involving a handful of patients showed an infusion of stem cells might help rebuild healthy hearts in heart attack survivors.

On March 7, Karpman joined that perilous club. A dermatologist in Camarillo, California, and a former marathon runner, the 66-year-old had a rigorous routine: eight to 10 miles of walking each day and a meticulous, meatless diet.

But that morning, sitting at his home computer, a pain kicked in.

"Within about 30 seconds, I was in extreme discomfort," recalls Karpman, who says it was worse than the kidney stones he once suffered. "I couldn't sit still. I mean even driving the car (to the hospital), I couldn't put a seat belt on; I'm just moving around, just trying to think of something else."

Karpman made it to Los Robles Hospital and Medical Center in Thousand Oaks, where doctors used stents to reopen an artery in his heart and save his life.

As he lay recovering, he took in some grim news: Nearly 20% of his heart muscle was dead, starved of oxygen. Dead heart tissue leaves a scar, interrupting the coordinated muscle action that makes the heart such an efficient pump.

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Heart attack damage may be reversible