An implantable delivery system has an inner shaft (20) with a device-carrying region (28) and an outer shaft (40) surrounding the inner shaft. A sheath (41) at a distal end of the outer shaft covers the device-carrying region when the outer shaft is in an advanced position. A sleeve (50) surrounding the outer shaft is in proximity to the sheath when the sleeve is in an advanced position. After insertion, the sleeve is retracted to increase flexibility of the distal end of the device. A handle (62) includes a control element for retracting the outer shaft and sheath relative to the inner shaft to release the implantable device. The sleeve may be fixed to the body of the handle when the sleeve is retracted. Engagement between the sleeve and an introducer at the insertion site can stabilize the handle and inner shaft against movement relative to the patient during retraction of the outer shaft.
