A method of implanting a heart valve prosthesis is disclosed. A valve is mounted within a support apparatus that is deformable between an expanded and a reduced cross-sectional condition. The prosthesis can be implanted into a patient's heart, such as during a direct vision procedure through a generally tubular implantation apparatus that maintains the prosthesis in its reduced cross-sectional condition until discharged from the tubular apparatus at a desired implantation site.