The largest trial done called the RESPECT trial randomized almost 1000 patients with cryptogenic stroke and a PFO to get either PFO closure with the Amplatzer PFO occluder or treatment with medicine to prevent stroke.  In follow-up the number of strokes in the group treated with PFO closure was about half that seen in the group treated with medicine. RESPECT TCT 2016 presentation Dr. Love wrote an editorial in the Journal of the American College of Cardiology in March 2016 on PFO closure.  Using all the available data at the time, an analysis of the data showed that PFO closure halved the event rate from 1%/year of stroke to 0.5%/year.   Meta analysis editorial Dr. Love