The neurology community has amassed a great deal of evidence that a certain type of heart defect known as a PFO is associated with an increased risk of stroke. This finding has prompted companies with transcatheter devices developed for a niche pediatric congenital defect market to migrate to adult stroke prevention. In the new field, the risk isn't so much technical--a history of device use in the pediatric market has obviated alot of this risk--as clinical. In stroke prevention, clinical trials not only have to prove a negative, which is always difficult, but will also have to confirm the role of PFOs in stroke, as yet scientifically unproven, at the same time as they validate devices.