A curve forming stent graft for curved vessels such as the thoracic arch. The stent graft has a tubular body zig zag self expanding stents fastened to and supporting the tubular body. The zig zag self expanding stents comprising struts and points between adjacent struts thereby defining proximal end points and distal end points. A temporary diameter constriction arrangement associated with the least some of the plurality of zig zag self expanding stents comprises a pair of adjacent distal end points being releasably retained adjacent each other whereby at rest the tubular body of the stent graft is in a substantially sawtooth form and when released in a curved configuration a distal end point of a stent overlaps a proximal end point of a distally adjacent stent to facilitate curvature of the stent graft in a curved vessel.