Implantable device for use in the human 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 end each have an opening to provide a fluid connection through the main body between first end and the second end; and a first membrane element arranged inside or at one end (3, 4) of the main body, wherein the membrane element is formed in such a manner that it allows a 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, a primary form, and a smaller ration of length to transverse expansion along the longitudinal axis of the main body in a second operating state, s 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 of interlocking winding and/or twisting and/or weaving in the manner of a woven and/or layered fabric and/or net; wherein the main body in the second operating state, the secondary form, has at the first end and/or second end at least one anchoring member (7, 8) extending in a radial direction of the main body for anchoring the device in a organ and/or a vessel, characterized in that the at least one anchoring member (7, 8) in the second operating state, the secondary form, of the main body has a first sub-portion and a second sub-portion, wherein the first sub-portion extends in a radial direction of the main body outwardly and the second sub-portion is folded backwards in a radial direction of the main body inwardly, in such a way, that the first sub-portion and the second sub-portion are folded onto another to a double-layer, wherein the backfolding of the at least one anchoring member (7, 8) is directed towards the middle of the main body. a main body having a first end and a second end, wherein the first end and the second end each have an opening to provide a fluid connection through the main body between first end and the second end; and a first membrane element arranged inside or at one end (3, 4) of the main body, wherein the membrane element is formed in such a manner that it allows a 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, a primary form, and a smaller ration of length to transverse expansion along the longitudinal axis of the main body in a second operating state, s 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 of interlocking winding and/or twisting and/or weaving in the manner of a woven and/or layered fabric and/or net; wherein the main body in the second operating state, the secondary form, has at the first end and/or second end at least one anchoring member (7, 8) extending in a radial direction of the main body for anchoring the device in a organ and/or a vessel, characterized in that the at least one anchoring member (7, 8) in the second operating state, the secondary form, of the main body has a first sub-portion and a second sub-portion, wherein the first sub-portion extends in a radial direction of the main body outwardly and the second sub-portion is folded backwards in a radial direction of the main body inwardly, in such a way, that the first sub-portion and the second sub-portion are folded onto another to a double-layer, wherein the backfolding of the at least one anchoring member (7, 8) is directed towards the middle of the main body.