Dan Merritt was trim, healthy and active, happily dividing his time among golf, gardening and grandchildren – the kind of person most people don’t think are at risk of strokes.

But he had at least three strokes, along with a few minor incidents, that doctors couldn’t explain. Determination and a sophisticated heart-monitoring device finally solved the mystery.

“Listen to your body,” said Mr. Merritt, 70, who lives in Newark, Delaware “It’s trying to tell you things. Don’t just shrug them off. If they’re persistent, you need to be persistent.”

Merritt, an Air Force veteran who retired from a career in the financial services industry, a few years ago started experiencing sudden pain in the back or shoulder when he was resting, occasional vertigo and blurred vision.

“I would pace for 15 minutes or so and it would go away,” he said. “I had no cholesterol problems, no high blood pressure. The doctors chalked it up to normal behavior and put me on a small aspirin dose for safety. I didn’t think there was a major problem. It was just something they weren’t catching.”

Then came the major problem. Three years ago on Halloween Merritt had what he now knows was a stroke in his doctor’s waiting room, but felt fine immediately, “so I didn’t make a big deal out of it.”

That evening, as he was getting ready to take his grandchildren trick-or-treating, the big deal struck.

“All of a sudden these things are happening,” he says. “You can’t talk, you’re drooling and your arm’s going numb. I motioned for my wife to come over because I didn’t want to alarm the kids.”

These were cryptogenic strokes, when a blocked blood vessel deprives blood to the brain and the cause of the blockage cannot be determined. That makes treatment more difficult and increases the chances of a recurrence.

His wife Barbara knew the FAST acronym for signs of a stroke – Face drooping, Arm weakness, Speech difficulty, Time to call 911 – and got him to the hospital. Five days and lots of tests later, doctors still couldn’t explain the strokes.

There were no lasting effects. But five months after that, in early 2014, Dan and Barbara were driving on a busy interstate near Baltimore when he began losing his vision.

“She said ‘Pull over!’ I said ‘Where?’ “ he recalls. “She said, ‘Anywhere!’ Then she drove me to the hospital.”

That earned him three more days of tests, no new answers, and more frustration.

“I didn’t sleep, I thought is it going to happen again?” Barbara said.  “The doctors didn’t know for sure what was causing the stroke. I felt like Dan was a walking time bomb.”

Finally his latest in a series of doctors, Raghuram Mallya M.D., had a suggestion. The usual workups, including tests with external heart monitors, revealed nothing, said Mallya, a cardiologist at Chester County Cardiology Associates in southeastern Pennsylvania. The next step was an insertable cardiac monitor.

“They’ve had implantable recorders for a long time,” he said. “But they were bigger devices and it was a surgical procedure. There’s more risk/benefit debate and it can be a harder sell to the patients.”

But a new monitor that had just been approved by the Food and Drug Administration made for an easier choice.

“They’re about the size of a pen cap and they’re placed just under the skin under local anesthesia,” Mallya said. “It can really lead to significant data and can really alter management.”

That’s just what happened.

For two weeks the device transmitted data about Merritt’s heart activity to a monitor next to his bed, and Mallya had his answer.

It was atrial fibrillation, commonly known as AFib, an irregular heartbeat that can cause blood clots. When those blood clots block arteries leading to the brain, a stroke results. The American Heart Association, which urges people to take the condition seriously, says untreated AFib increases the risk of strokes by five times and doubles the risk of heart-related deaths.

Merritt didn’t need persuaded to take care of his health, and had kept a diary of his incidents for years.

“If something’s not right, keep getting it checked out,” he said. “I was really relieved to get this figured out. They can control it through chemicals.”

Those chemicals include blood-thinners, blood vessel relaxers and beta-blockers, and they’ve kept Merritt healthy and stroke-free for two-and-a-half years. Sadly, his good fortune and understanding of the danger of strokes were reinforced last year when a good friend suffered a stroke, fell and broke vertebrae and became incapacitated.

“It could just as easily have been me,” he said.

Barbara agrees. “I know how incredibly lucky he is to be telling his story and to be with us. And I know how lucky I am to have him here with me.”