A prosthesis delivery system comprises a sheath defining an axial direction； at least one tether movable axially relative to the sheath； and a holder movable axially within the sheath, configured to constrain radially the tether(s). Collapsing the prosthesis to a collapsed state in the sheath involves constraining radially with a holder the tether(s), attached to the prosthesis； and moving the tether(s) and the holder axially within the sheath such that the prosthesis is forced to collapse into the sheath and the holder is retracted into the sheath.
