The invention relates to an assembly comprising a ring having, viewed in its axial direction, a distal side and a proximal side； and a sleeve which is slideable with respect to the ring from an overlapping position accommodating the ring inside the sleeve, in proximal direction, into an exposing position in which the ring is released outside the sleeve. The ring has, at its distal end and proximal end, anchoring elements for attaching the ring in a passage surrounded by body tissue, in particular blood vessel tissue. The anchoring elements have an anchoring position in which they protrude in radial outward direction with respect to the ring. The distal anchoring elements are bendable from said anchoring position counter to a spring force into a fitting position. The sleeve is provided at its distal end with axial fingers. A space is left between neighbouring axial fingers. The axial fingers are provided in such a manner that, when the sleeve is in overlapping position, each axial finger overlaps a respective distal anchoring element to keep said respective anchoring element in the fitting position and allow bending the anchoring elements back from the fitting position into the anchoring position by the effect of the spring force when the sleeve is slid from the overlap position to the exposing position.
