A stent graft for implantation into a thoracic arch into a which a side arm can be deployed. The stent graft comprises a primary prosthesis (20) with a fenestration (85) and graft material tube (87) for receiving a second prosthesis. The graft material tube (87) includes at least a portion which extends into the primary prosthesis (20) and which is angled in a proximal direction to direct blood flowing from the heart to the branch artery. The graft material tube (87) also comprises an aperture (88) to accommodate a guide wire passing through the primary prosthesis (20) from a distal location into the graft material tube (87) and into the branch artery. The guide wire is configured to facilitate placement of a secondary prosthesis in the branch artery.
