A delivery system and method for implanting a stent graft includes a flexible sheath that defines openings distributed longitudinally and wherein substantial alignment of the openings along a longitudinal axis of a guidewire catheter radially constrict the flexible sheath. The flexible sheath includes at least one fenestration. A ligature extends through the openings of the flexible sheath and causes the openings to be substantially aligned, thereby constraining the flexible sheath. The ligature is proximally retractable from the openings to thereby release the flexible sheath from a radially constricted configuration.
