Apparatus is described including a ventricular assist device (20) that includes an impeller (50) configured to be placed inside a left ventricle of a subject, and a frame (34) configured to be disposed around the impeller (50). A motor (74) drives the impeller (50) to pump blood from the left ventricle to an aorta of the subject, by rotating the impeller (50). The entire impeller (50) is configured to undergo axial back-and-forth motion with respect to the frame (34), in response to cyclical changes in a pressure difference between the left ventricle and the aorta. Other applications are also described.
