An implant assembly is implanted in vivo within a vascular system in which avessel divides at a furcation into two sub-vessels, with smaller diameters. Animplant assembly is released into a vessel e.g. a pulmonary arterial vessel.The assembly has a diameter smaller than or substantially equal to the innerdiameter of the vessel and larger than the inner diameters of the sub-vessels.The implant assembly moves downstream along with the blood flow. Reaching thefurcation where the vessel divides, the implant assembly is too large and notsufficiently compliant to fit through either of the smaller branch vessels,thus lodges at the furcation, prevented from moving downstream by it's sizeand stiffness and upstream by the blood flow. Alternatively, the implantassembly, upon release, travels down a narrowing vessel until an interferencefit is created between the anchor structure and the vessel wall, therebypreventing further distal movement.
