A delivery device for a collapsible prosthetic heart valve, the delivery device comprising: an operating handle, including: a housing defining a movement space therein; a carriage assembly moveable in a longitudinal direction within the movement space; a deployment actuator coupled to the housing and rotatable relative to the housing; and a coupling assembly rotationally fixed to the deployment actuator, the coupling assembly having an engaged position in which rotation of the deployment actuator moves the carriage assembly in the longitudinal direction, and a disengaged position in which rotation of the deployment actuator does not move the carriage assembly in the longitudinal direction; and a catheter assembly, including: a first shaft around which a compartment is defined, the first shaft being operatively connected to the housing, the compartment being adapted to receive the valve in an assembled condition; and a distal sheath operatively connected to the carriage assembly, the distal sheath being moveable between a closed condition covering the compartment and an open condition uncovering the compartment for deployment of the valve, wherein movement of the carriage assembly in the longitudinal direction in the movement space moves the distal sheath between the closed condition and the open condition, and wherein the carriage assembly includes a threaded rod extending from a body of the carriage assembly and into threaded engagement with the coupling assembly characterized in that the coupling assembly includes a split nut having a plurality of threaded split nut portions (64a, 64b), the split nut portions each being linearly slideable away from one another and away from the threaded rod, the split nut having an engaged position in which threads of the split nut portions are engaged with the threaded rod and a disengaged position in which the threads of the split nut portions do not engage the threaded rod an operating handle, including: a housing defining a movement space therein; a carriage assembly moveable in a longitudinal direction within the movement space; a deployment actuator coupled to the housing and rotatable relative to the housing; and a coupling assembly rotationally fixed to the deployment actuator, the coupling assembly having an engaged position in which rotation of the deployment actuator moves the carriage assembly in the longitudinal direction, and a disengaged position in which rotation of the deployment actuator does not move the carriage assembly in the longitudinal direction; and a housing defining a movement space therein; a carriage assembly moveable in a longitudinal direction within the movement space; a deployment actuator coupled to the housing and rotatable relative to the housing; and a coupling assembly rotationally fixed to the deployment actuator, the coupling assembly having an engaged position in which rotation of the deployment actuator moves the carriage assembly in the longitudinal direction, and a disengaged position in which rotation of the deployment actuator does not move the carriage assembly in the longitudinal direction; and a catheter assembly, including: a first shaft around which a compartment is defined, the first shaft being operatively connected to the housing, the compartment being adapted to receive the valve in an assembled condition; and a distal sheath operatively connected to the carriage assembly, the distal sheath being moveable between a closed condition covering the compartment and an open condition uncovering the compartment for deployment of the valve, a first shaft around which a compartment is defined, the first shaft being operatively connected to the housing, the compartment being adapted to receive the valve in an assembled condition; and a distal sheath operatively connected to the carriage assembly, the distal sheath being moveable between a closed condition covering the compartment and an open condition uncovering the compartment for deployment of the valve, wherein movement of the carriage assembly in the longitudinal direction in the movement space moves the distal sheath between the closed condition and the open condition, and wherein the carriage assembly includes a threaded rod extending from a body of the carriage assembly and into threaded engagement with the coupling assembly characterized in that the coupling assembly includes a split nut having a plurality of threaded split nut portions (64a, 64b), the split nut portions each being linearly slideable away from one another and away from the threaded rod, the split nut having an engaged position in which threads of the split nut portions are engaged with the threaded rod and a disengaged position in which the threads of the split nut portions do not engage the threaded rod