An occlusion device for the closure of atrial or ventricular septal defects, for the closure of patent ductus arteriosus, patent foramen ovale, or other vascular defects. The occlusion device comprises a center section extending in an axial direction, with upper and lower stranded wire fixation devices emanating from the center section. The stranded wire fixation devices have been heat treated and formed with a shape memory. The stranded wire fixation devices are formed of multiple wire strands and have atraumatic tips. Attached to the fixation devices are heparin treated sheets, which serve to occlude the opening and significantly reduce the occurrence of thrombosis at the device.