This hole is either a heart defect (atrial septal defect) or an enlarged natural opening (foramen ovale) that is supposed to close soon after birth.

CNN: Tricuspid atresia

One theory on why cryptogenic strokes occur in younger people in their 40s and 50s is that the flap known as a patent foramen ovale, or PFO can allow blood clots to reach the brain, physicians say.

WSJ: Doctors Debate Whether Strokes Be Prevented With a Heart-Plug Procedure

Some of them may interpret the data as supporting closure of a patent foramen ovale as a viable therapeutic option, even while conceding the failure of trials to show the superiority of closure over medical therapy.

FORBES: Controversial PFO Closure Trials Published In NEJM

The PC T rial (Clinical Trial Comparing Percutaneous Closure of Patent Foramen Ovale Using the Amplatzer PFO Occluder with Medical Treatment in Patients with Cryptogenic Embolism) randomized 414 patients with PFO who had had an ischemic stroke, TIA, or a peripheral thromboembolic event to either medical therapy or PFO closure with the Amplatzer PFO Occluder.

FORBES: Controversial PFO Closure Trials Published In NEJM