Abstract: Described are occlusion instruments (1, 2, 3, 4) comprising bioresorbable and thermoplastically deformable polymers with or without shape memory characteristics, which contain radiopaque building groups in the repeat units of the polymer chains and/or are modified with bioresorbable, radiopaque nanoparticles. The polymers display sufficient strength and deformability, good bioresorbability and sufficient visibility in radiance and are particularly useful for producing metal-free occlusion instruments for closing defects of the septum in the heart, the positioning of which being monitorable using routine diagnostic methods.