Disclosed are an instrument, valve prosthesis and procedure for the minimally invasive implantation of a sutureless anti-reflux valve in a patient for the treatment of gastroesophageal reflux disease. A prosthesis is provided that comprises a cylindrical housing, a mounting ring and a one-way anti-reflux valve depending from the mounting ring. The cylindrical housing is constructed of a memory material that can be fixed in the gastroesophageal junction. The mounting ring and the anti-reflux valve are fixed within the housing.