occluding the left subclavian artery stent 17 on the stent graft is of the zig zag or z stent type and is shown dotted in fig6 for the sake of clarity the stent graft is schematically depicted in a diameter reduced state by the use of a diameter reducing arrangement generally shown as 16 the diameter reducing arrangement includes release wires 18 extending down each side of the stent graft in a helical manner in opposite directions from a distal end 14 to the proximal end 12 the release wire 18 is stitched in and out of the graft material of the stent graft to maintain it in position a further release wire is in a similar configuration on the other side of the stent graft at intervals along the length of the stent graft threads 22 and 24 are looped around the release wire and extended in opposite circumferential directions as discussed in detail with reference to fig5 a and 5b to hold the stent graft in a partially diameter reduced state the diameter reducing arrangements on each side therefore extend in a part helical manner from one end of the stent graft to the other the stent graft is retained onto a delivery device 42 at its proximal end 12 just distal of a nose cone dilator 50 on a guide wire catheter 52 which passes through the stent graft 10 retention is by fastening struts of the proximal most stent to a trigger wire not shown by means of a suture 54 as is explained in pct patent publication wo 03 101518 entitled u201c trigger wire system for a prosthesis deployment device u201d the teaching of which is incorporated herein in.