Apparatus for use with a portion of a body of a subject, comprising: an implantable element, comprising a shape-memory material having a transformation temperature, the implantable element configured to be implanted in the portion, and to perform a first therapeutic function with respect to the portion when the shape-memory material is in a first shape, and while the implantable element is implanted in the portion; and an energy applicator, configured to change the shape-memory material from the first shape to a second shape, by raising a temperature of the shape-memory material to the transformation temperature, the implantable element being configured to perform a second therapeutic function with respect to the portion when the shape-memory material is in the second shape, and while the implantable element is implanted in the portion, characterized in that: the energy applicator is configured to be disposed outside the subject's body and to radiate energy from outside the subject's body to the implantable element implanted in the subject's body; and the implantable element is shaped as: a cylindrical stent when the shape-memory material is in the first shape to open a blood vessel when performing the first therapeutic function; and a venturi tube when the shape-memory material is in the second shape to cause a controlled narrowing of the blood vessel and generate a new blood vessel that circumvents a region of the blood vessel within which the implantable element is implanted when performing the second therapeutic function. an implantable element, comprising a shape-memory material having a transformation temperature, the implantable element configured to be implanted in the portion, and to perform a first therapeutic function with respect to the portion when the shape-memory material is in a first shape, and while the implantable element is implanted in the portion; and an energy applicator, configured to change the shape-memory material from the first shape to a second shape, by raising a temperature of the shape-memory material to the transformation temperature, the implantable element being configured to perform a second therapeutic function with respect to the portion when the shape-memory material is in the second shape, and while the implantable element is implanted in the portion, characterized in that: the energy applicator is configured to be disposed outside the subject's body and to radiate energy from outside the subject's body to the implantable element implanted in the subject's body; and the implantable element is shaped as: a cylindrical stent when the shape-memory material is in the first shape to open a blood vessel when performing the first therapeutic function; and a venturi tube when the shape-memory material is in the second shape to cause a controlled narrowing of the blood vessel and generate a new blood vessel that circumvents a region of the blood vessel within which the implantable element is implanted when performing the second therapeutic function. the energy applicator is configured to be disposed outside the subject's body and to radiate energy from outside the subject's body to the implantable element implanted in the subject's body; and the implantable element is shaped as: a cylindrical stent when the shape-memory material is in the first shape to open a blood vessel when performing the first therapeutic function; and a venturi tube when the shape-memory material is in the second shape to cause a controlled narrowing of the blood vessel and generate a new blood vessel that circumvents a region of the blood vessel within which the implantable element is implanted when performing the second therapeutic function.