Apparatus is provided including an implantable structure (22), including a flexible sleeve (26), having first and second sleeve ends (49, 51), a contracting assembly (40), which is configured to longitudinally contract the sleeve (26). The contract assembly (40) includes a contracting mechanism (28), which is at a first site of the sleeve (26)； and a longitudinal contracting member (30), having (a) a first member end, (b) a second member end (53), coupled to the sleeve (26) at a second site longitudinally between the first site and the second sleeve end (49 or 51), exclusive. A force -distributing element (540) is couplable to the sleeve (26) in a vicinity of the second sleeve end (49 or 51), element (540) is configured to distribute a contraction force by the contracting member (30) between the second member end (53) and the second sleeve end (49 of 51). Other applications are also described.
