Dr. Fermin Garcia of Penn Medicine is in national trials of the Watchman.
It's designed for patients with atrial fibrillation - a condition in which the chambers of the heart beat out of sync.
The irregular rhythm lets blood pool in a sac inside the heart.
Dr. Garcia explains that, "Blood can sit there and clot and break off. From there, it can go up to the brain and that's what causes a stroke."
Through a catheter, the Watchman is delivered up into the heart, and inserted into that sac, and opened.
It stays there, and over time, tissue grows over it, keeping blood from pooling there.
The goal is to see if it works as well as the standard blood thinner - Coumadin -- in preventing strokes.
Although the Watchman trial is still underway, Dr. Garcia says, "There are many patients in the united states who've been able to get off Coumadin after the procedure."
Jim Greaves was diagnosed with a-fib in 2006, after he had a scary episode of slurred words. Doctors said he'd has a TIA, or transient eschemic attack - a mini-stroke that often passes in minutes. Since then, he'd been on blood thinners, but this active basketball referee wasn't happy about it.
"I'd get bruises in places I never bumped," he told Action News.
He also didn't like the restrictions on his diet, particularly salads, that had to be followed on the blood thinners.
But so far, he's happy with the Watchman.
"You know how when you crouch, to get something out from under the couch, or under the medicine cabinet, and you get up and you get that real dizzy feeling? i was getting that on a regular basis with the coumadin. i haven't had that since," he says.
Dr. Garcia says tests of the Watchman will continue till later this year.