The invention relates to an implantable device for use in the human and/or animal body to replace an organ valve, comprising a main body having a first end and a second end, wherein the first end and the second each have an opening to provide a fluid connection through the main body between the first end and the second end; a first membrane element arranged inside or at one end of the main body, wherein the membrane element is formed in such a manner that it allows the fluid connection through the main body in a first flow direction and blocks the same in a second flow direction opposite the first flow direction; wherein the main body has a large ratio of length to transverse expansion along the longitudinal axis of the main body in a first operating state (primary form) and a smaller ratio of length to transverse expansion along the longitudinal axis of the main body in a second operating state (secondary form); and wherein the main body can be reversibly transferred from the secondary form to the primary form counter to elastic material forces by the application of a force; and wherein the main body is formed from a single wire-like element or from a plurality of wire-like elements connected to each other by means interlocking winding and/or twisting and/or weaving in the manner of a woven and/or layered fabric and/or net.