The invention relates to a self-expanding device, particularly an implant, for closing defect openings in the human or animal body, which device, in a first state, has the shape of an elongated tube (2) with slotted segments and, in a second state, has a shortened shape with formation of at least one open or substantially closed hollow structure (3) of considerable transverse extent, where in the slotted segments of the tube (2) form individual webs (16) that are each connected to adjacent webs (16), such that a net-like overall structure is obtained in the second state.