Disclosed is a side branch vessel device, which is placed in the side branch vessel before the deployment of a stent graft in the main vessel. The side branch vessel device either comprises means to create a fenestration in the stent graft when deployed, or otherwise, such means are introduced adjacent thereto. Once the stent graft is deployed, the side branch vessel device is transformed to an opened configuration, which aids in holding the fenestration at the point where the side branch vessel branches off from the main vessel.