Catheter-supported therapeutic and diagnostic tools can be introduced into a patient body with a sheath slidably disposed over the tool. Once the tool is aligned with a target tissue, a first fluid-driven actuator can move the sheath axially from over the tool, for example, to allow a stent, stent-graft, prosthetic valve, or other self-expanding tool, to expand radially within the cardiovascular system, without having to transmit large deployment forces along the catheter shaft and sheath from outside the patient. A second fluid-driven actuator can be arranged in opposition to the first actuator to control release of the expanding tool or to recapture the tool within the sheath. The first and/or second actuators may comprise a balloon having a diameter larger than the sheath to provide the desired deployment and recapture forces with moderate fluid pressure.
