An artery can be occluded by implanting an occlusion implant within a subintimal space within a wall of the artery. As an example, a catheter having a side port just proximal of an inflatable balloon disposed near a distal end of the catheter can be advanced through the artery to a site at which an occlusion is desired. The inflatable balloon can be inflated and a guidewire can be advanced through a lumen of the catheter, out of the side port and into a subintimal space of the artery, with the inflated inflatable balloon guiding the guidewire towards the artery wall. An occlusion implant can be advanced over the guidewire into the subintimal space and the guidewire can be withdrawn, leaving the occlusion implant positioned within the subintimal space.