Abstract: An implantable device which is suited for implantation into a human or animal heart for receiving and removably holding a valve prosthesis is described. The device comprises a ring structure which is adapted to be fixed to the tissue around the orifice of a heart valve after excision of the diseased or damaged natural valve has been effected. In use, the ring structure is fixed in place and then the appropriate valve prosthesis is attached to the ring. When the valve prosthesis fails and has to be replaced with a new prosthesis, the damaged prosthesis can be detached from the ring allowing a replacement prosthesis to be fixed to the ring without affecting the connection between ring structure and tissue.