An instrument for positioning a cardiac valve prosthesis in a vessel includes a wire element (10) to slidingly guide the valve prosthesis towards an implantation site and an expandable element (12) coupled to the wire element. The expandable element is expandable in the vessel to position the wire element in association with the implantation site. A method for positioning a cardiac valve prosthesis includes securing a delivery instrument at an appropriate location at the implantation site and delivering the valve prosthesis to the implantation site using the delivery instrument.