A prosthetic heart valve delivery system, comprising: a main catheter having a main shaft adapted to extend through a patient's vasculature; a valve-retaining mechanism coupled to a distal end of the main shaft; a prosthetic heart valve coupled to the valve-retaining mechanism; characterized in that the system further comprises: a torque catheter comprising a torque shaft extending within the main shaft and having a distal end connected to a screw mechanism; and a valve sheath coupled to the screw mechanism and configured to receive the prosthetic heart valve in a radially compressed state for delivery to the heart through the patient's vasculature; wherein rotation of the torque shaft and the screw mechanism in one direction relative to the main shaft and the valve sheath is effective to cause proximal movement of the valve sheath relative to the prosthetic heart valve to retract the valve sheath and deploy the prosthetic heart valve from a distal end of the valve sheath, wherein the valve retaining mechanism is configured to form a releasable connection between the prosthetic heart valve and the main shaft, which connection can be released after the prosthetic heart valve is deployed from the valve sheath. a main catheter having a main shaft adapted to extend through a patient's vasculature; a valve-retaining mechanism coupled to a distal end of the main shaft; a prosthetic heart valve coupled to the valve-retaining mechanism; characterized in that the system further comprises: a torque catheter comprising a torque shaft extending within the main shaft and having a distal end connected to a screw mechanism; and a valve sheath coupled to the screw mechanism and configured to receive the prosthetic heart valve in a radially compressed state for delivery to the heart through the patient's vasculature; wherein rotation of the torque shaft and the screw mechanism in one direction relative to the main shaft and the valve sheath is effective to cause proximal movement of the valve sheath relative to the prosthetic heart valve to retract the valve sheath and deploy the prosthetic heart valve from a distal end of the valve sheath, wherein the valve retaining mechanism is configured to form a releasable connection between the prosthetic heart valve and the main shaft, which connection can be released after the prosthetic heart valve is deployed from the valve sheath. a torque catheter comprising a torque shaft extending within the main shaft and having a distal end connected to a screw mechanism; and a valve sheath coupled to the screw mechanism and configured to receive the prosthetic heart valve in a radially compressed state for delivery to the heart through the patient's vasculature; wherein rotation of the torque shaft and the screw mechanism in one direction relative to the main shaft and the valve sheath is effective to cause proximal movement of the valve sheath relative to the prosthetic heart valve to retract the valve sheath and deploy the prosthetic heart valve from a distal end of the valve sheath, wherein the valve retaining mechanism is configured to form a releasable connection between the prosthetic heart valve and the main shaft, which connection can be released after the prosthetic heart valve is deployed from the valve sheath.