Apparatus and methods are described including identifying a subject as suffering from a condition selected from the group consisting of: cardiac dysfunction, congestive heart failure, reduced renal blood flow, increased renal vascular resistance, arterial hypertension, and kidney dysfunction. In response thereto, blood pressure within a renal vein (32) of the subject is reduced, by placing a blood pump (150) inside the subject's renal vein and activating the impeller to pump blood from the renal vein into the subject's vena cava (26). Other applications are also described.