Apparatus and methods are described including identifying a subject as suffering from cardiac dysfunction, congestive heart failure, reduced renal blood flow, increased renal vascular resistance, arterial hypertension, and/or kidney dysfunction, and, in response thereto, reducing blood pressure within a renal vein of the subject, by activating at least one impeller to pump blood from the renal vein into a vena cava of the subject, by the impeller rotating.