The foramen ovale is an opening in the interatrial septum. It results from an incomplete coverage of the ostium secundum. In 10 to 24% of the general population incomplete fibrosis of the interatrial septum is a clinical finding and is defined as a patent foramen ovale (PFO). The Nit-Occlud® PFO umbrella is a permanent implant for closing PFOs that is implanted in the PFO using minimally invasive catheter technology. The umbrella is made from Nitinol, a material with superelastic properties, which, in its relaxed state, has the form of a double umbrella. This is a single-center, non-comparative, prospective interventional clinical investigation involving 1 center in Germany to assess the effectiveness, safety and practicability of implantation of the Nit-Occlud PFO® Closure Device.