Abstract: The invention relates to a device which can be implanted inside a vessel to form a blood filter there. The device comprises a structure (7) disposed along the axis (3) of a surface of revolution, radially to which axis the structure can be expanded or compressed such that, in its expanded position, it can contact the interior of the vessel. Means (15, 17) for stressing at least a portion of this structure "in situ" are further provided either to move it closer to the axis of the surface of revolution, forming a constriction area for filtering the blood, or to move it away therefrom, thus varying this filtering capacity. Application to temporary filters which can be implanted "for life".