Apparatus and methods are described including a valve (34) that includes valve leaflets (33) and a non-branched valve frame (31) configured to support the valve leaflets, the frame defining a single longitudinal axis thereof, the longitudinal axis being a generally straight line along a full length of the frame. The valve (34) is placed at least partially within a renal vein of a subject. The valve defines an open state thereof in which the valve leaflets (33) allow generally unimpeded antegrade blood flow therethrough, and a closed state thereof in which the valve leaflets (33), in a passive manner, reduce venous pressure within the renal vein relative to central venous pressure of the subject. Other applications are also described.