A delivery system (100; 200) for controlled deployment of a replacement valve in a patient, the delivery system comprising: a first member (118, 124, 130, 132; 124, 130, 218, 232) configured to at least partially restrain a first end of the replacement valve; a second member (114, 116; 214) configured to at least partially restrain a second end of the replacement valve; a tether configured to at least partially encircle the replacement valve and radially restrain at least a portion of the replacement valve after the second member (114, 116; 214) has been removed from the second end of the replacement valve but with the first member (118, 124, 130, 132; 124, 130, 218, 232) still at least partially restraining the first end of the replacement valve; and a tether retention assembly (122, 129, 134; 134, 222, 229) configured to restrain the tether such that the tether can be tensioned to restrain at least a portion of the replacement valve, wherein the tether retention assembly (122, 129, 134; 134, 222, 229) comprises an inner component and an outer component (129; 229), the outer component (129; 229) being configured to cooperate with the inner component to restrain the tether, wherein the first member (118, 124, 130, 132; 124, 130, 218, 232) comprises a first shaft and the second member (114, 116; 214) comprises a second shaft, the second shaft being positioned over the first shaft and slidable relative to the first shaft, wherein the first member (118, 124, 130, 132; 124, 130, 218, 232) further comprises an inner retention ring (132; 232) configured to engage the first end of the replacement valve, the inner retention ring (132; 232) connected to a distal portion of an inner retention shaft, the inner retention shaft being positioned between the first shaft and the second shaft and being slidable relative to the first shaft, characterized in that the tether retention assembly (122, 129, 134; 134, 222, 229) further comprises a locking shaft (122; 222), the outer component (129; 229) of the tether retention assembly being coupled to the distal end of the locking shaft (122; 222). a first member (118, 124, 130, 132; 124, 130, 218, 232) configured to at least partially restrain a first end of the replacement valve; a second member (114, 116; 214) configured to at least partially restrain a second end of the replacement valve; a tether configured to at least partially encircle the replacement valve and radially restrain at least a portion of the replacement valve after the second member (114, 116; 214) has been removed from the second end of the replacement valve but with the first member (118, 124, 130, 132; 124, 130, 218, 232) still at least partially restraining the first end of the replacement valve; and a tether retention assembly (122, 129, 134; 134, 222, 229) configured to restrain the tether such that the tether can be tensioned to restrain at least a portion of the replacement valve, wherein the tether retention assembly (122, 129, 134; 134, 222, 229) comprises an inner component and an outer component (129; 229), the outer component (129; 229) being configured to cooperate with the inner component to restrain the tether, wherein the first member (118, 124, 130, 132; 124, 130, 218, 232) comprises a first shaft and the second member (114, 116; 214) comprises a second shaft, the second shaft being positioned over the first shaft and slidable relative to the first shaft, wherein the first member (118, 124, 130, 132; 124, 130, 218, 232) further comprises an inner retention ring (132; 232) configured to engage the first end of the replacement valve, the inner retention ring (132; 232) connected to a distal portion of an inner retention shaft, the inner retention shaft being positioned between the first shaft and the second shaft and being slidable relative to the first shaft, characterized in that the tether retention assembly (122, 129, 134; 134, 222, 229) further comprises a locking shaft (122; 222), the outer component (129; 229) of the tether retention assembly being coupled to the distal end of the locking shaft (122; 222).