A tissue anchor (20) comprises a helical tissue-coupling element (30) disposed about a longitudinal axis (32) thereof and having a distal tissue-penetrating tip (34). The helical tissue-coupling element (30) has: a first axial stiffness along a first axial portion (60) of the helical tissue-coupling element (30)； a second axial stiffness along a second axial portion (62) of the helical tissue-coupling element (30) more distal than the first axial portion (60), which second axial stiffness is greater than the first axial stiffness； and a third axial stiffness along a third axial portion (64) more distal than the second axial portion (62), which third axial stiffness is less than the second axial stiffness. Other embodiments are also described.
