Abstract: An implantable device is described for detecting an expansion which is an elastic deformation of an intracorporeal vessel wall. The device comprises a support structure which contains dielectric polymer, has surface elasticity and can be applied directly or indirectly to the vessel wall, which provides at least one capacitive electrode arrangement, of which the assignable electrical capacitance can be influenced by an elastic deformation of the support structure. The electrode arrangement includes at least two electrodes each consisting of an electrically conductive polymer. The electrodes each define at least one side an intermediate space that influences the electrical capacitance of the electrode arrangement. The space is filled with the dielectric polymer of the support structure.