Apparatus and methods are described for improving renal function of a patient, including mechanically occluding the patient's inferior vena cava downstream of the renal vein ostium to form an upstream region and a downstream region of the inferior vena cava, and mechanically pumping blood through the inferior vena cava from the upstream region to a discharge location in the downstream region while the inferior vena cava is occluded, wherein the blood remains in the inferior vena cava while being mechanically pumped. Other applications are also described.