An instrument for the surgical removal of a defective heart valve. The instrument has elements that can be collapsed, in which the instrument cutting elements are collapsed when the instrument is introduced into the surgical field and are covered by means of contact protective sheaths. The instrument cutting elements are formed as cutting ring halves that can fold in around a hinge axis, these cutting ring halves being elastically deformable during the folding-in process, whereby their deformation is achieved by fish joints that also serve to aid in mutually moving the contact protective sheaths onto each of two body members.
