John Chenevert knew there was a chance he was going to all this trouble for nothing.

When the Richfield resident volunteered, he was told that some patients would get real stem cells, others a ­placebo.

Chenevert, now 69, figured it was worth the gamble. He's been fighting heart disease for 40 years.

"I had read quite a bit about stem cells," he said, and found the whole idea intriguing. "I firmly believe that life as we know it today can be extended."

Chenevert was only 29 when he had his first heart attack and doctors discovered a genetic defect: One artery was missing. Eventually, two more heart attacks (at ages 44 and 52) caused so much damage that he was told he would need a heart transplant. He was plagued by chronic, crippling bouts of chest pain.

The experiment was designed to take stem cells from a patient's own bone marrow, and see if they could improve blood flow to the heart. But he didn't feel any better. A year later, Chenevert learned that he'd gotten a placebo.

Cravatt Stanley Cravatt

When the doctors offered to do it again, this time with real stem cells, he agreed. Over time, tests showed some new blood vessels near his heart. Today, he says, the chest pain is less severe and less frequent. "It hasn't totally gone away," he said, but "it's a big change."

•••

Stanley Cravatt woke up on the morning of his father's funeral and called an ambulance. He was having a heart attack. Just like the one that killed his dad.

"I was 42," he said. His wife was pregnant with their first child.

That was 1990. Since then, the Texas-born cartographer has had three more heart attacks, quadruple-bypass surgery and a pacemaker. He's also hiked Big Bend National Park, climbed the Andes, and raised two sons to adulthood.

Cravatt, who moved to Minneapolis in 2010, said he didn't hesitate when he was offered a spot in a stem-cell study at Abbott Northwestern in January.

"I felt I had nothing to lose," he said. After his wife, a law professor, and his pastor read the brochure, both gave their blessings.

He was hospitalized overnight to allow doctors to remove fat cells from his stomach, where the stem cells would be derived. The joke in the family was how they'd find any fat cells on Cravatt's lean body.

He won't know for years whether he got a placebo or stem cells. But at 65, he doesn't seem troubled either way.

"If they find out just one thing that will improve someone else's heart problem, it's been worth it," Cravatt said.

Maura Lerner • 612-673-7384