Apparatus and methods are described including a tube configured to traverse a subject's aortic valve. A frame is disposed within a portion of the tube, and a plurality of winged projections are coupled to the frame. An impeller is disposed inside the tube, the impeller including at least one helical elongate element, and a film of material supported at least partially by the helical elongate element. The impeller is rotated, such as to pump blood from the subject's left ventricle to the subject's aorta. Blood flow that is generated by the rotation of the impeller is rectified, by using the winged projections to direct blood flow toward a direction of the longitudinal axis of the tube. Other applications are also described.