An apparatus for controlling a flow of blood in a blood vessel formed by a tissue wall of a patient's blood vessel comprises an implantable constriction device for gently constricting (i.e. without substantially hampering the blood circulation in the tissue wall) at least one portion of the tissue wall to influence the flow in the blood vessel, and a stimulation device for stimulating the wall portion of the tissue wall. A control device controls the stimulation device to stimulate the wall portion, as the constriction device constricts the wall portion, to cause contraction of the wall portion constricted by the constriction device to further influence the flow in the blood vessel. The apparatus can be used for stabilizing, treating or controlling an aneurysm, with a low risk of side- effects, such as injuring the blood vessel or causing embolism.
