The invention relates to an occluder for closing a passage in a circulatory system comprising an expandable fixation unit for fixing the occluder on the passage, wherein the occluder can be transferred in the passage from a compact appearance into an expanded appearance. The occluder has a distal and a proximal axial part, in which the fixation unit is pivotally held. According to the invention, the fixation unit comprises distal fixation arms and proximal fixation arms, wherein the distal fixation arms are pivotally held in the distal axial part and the proximal fixation arms are pivotally held in the proximal axial part. The distal and the proximal fixation arms have free ends, which are interconnected by means of connecting members that can be moved relative to the fixation arms, wherein in each case a distal fixation arm is connected to a proximal fixation arm located diagonally opposed thereto. Said occluder is suited in particular for closing a ventricular septal defect (VSD).
