A stent for occluding the human ductus arteriosus comprises a length of wire of shape memory effect or superelastic material which is expandable from a relatively straightened state for introduction into the patient, to an occluding state wherein the wire defines an occluding anchor part (10), and spiral anchor part (12) and a straight linking part (14). In the occluding anchor part (10), the wire has adopted a series of turns extending over the cross-sectional area of the occluding anchor part (10).