DEFENSE-PFO was a multicenter randomzed controlled trial conducted in South Korea. Subjects with prior stroke and PFO were randomized to PFO closure with the Amplatzer PFO Occluder (Abbott, Lake Bluff, IL) or medical therapy, which included aspirin, aspirin + clopidogrel, aspirin + cilostazol, or warfarin. At a mean of 2.8 years of follow-up, the PFO closure group had a lower rate of stroke, cardiovascular death, or major bleeding. The trial was stopped early, with only 120 patients, due to overwhelming evidence of benefit to PFO closure. Anatomic PFO features associated with elevated stroke risk were identified: atrial septal aneurysm, wide PFO opening, short tunnel length, and large shunt.