Apparatus comprising: a left-ventricular assist device configured to assist left-ventricular functioning of a subject, the left-ventricular assist device comprising: a tube configured to traverse an aortic valve of a subject, such that a proximal end of the tube is disposed within an aorta of the subject and a distal end of the tube is disposed within a left ventricle of the subject; a frame disposed within at least a portion of the tube, the frame defining a plurality of cells, the frame being configured such that, in a non-radially-constrained configuration of the frame, the frame comprises a generally cylindrical portion ; an inner lining that lines at least some of the cylindrical portion of the frame ; and an impeller disposed inside the frame such that, in a non-radially-constrained configuration of the impeller , at a location at which a span of the impeller is at its maximum, the impeller is disposed within the cylindrical portion of the frame , such that a gap (G) between an outer edge of the impeller and the inner lining is less than 1 mm, the impeller being configured to rotate such as to pump blood from the left ventricle to the aorta, the apparatus characterized in that : a width (CW) of each of the cells within the cylindrical portion as measured around a circumference of the cylindrical portion is less than 2 mm, and the impeller is configured to be stabilized with respect to the frame , such that, during rotation of the impeller , the gap (G) between the outer edge of the impeller and the inner lining is maintained and is substantially constant. a tube configured to traverse an aortic valve of a subject, such that a proximal end of the tube is disposed within an aorta of the subject and a distal end of the tube is disposed within a left ventricle of the subject; a frame disposed within at least a portion of the tube, the frame defining a plurality of cells, the frame being configured such that, in a non-radially-constrained configuration of the frame, the frame comprises a generally cylindrical portion ; an inner lining that lines at least some of the cylindrical portion of the frame ; and an impeller disposed inside the frame such that, in a non-radially-constrained configuration of the impeller , at a location at which a span of the impeller is at its maximum, the impeller is disposed within the cylindrical portion of the frame , such that a gap (G) between an outer edge of the impeller and the inner lining is less than 1 mm, the impeller being configured to rotate such as to pump blood from the left ventricle to the aorta, the apparatus characterized in that : a width (CW) of each of the cells within the cylindrical portion as measured around a circumference of the cylindrical portion is less than 2 mm, and the impeller is configured to be stabilized with respect to the frame , such that, during rotation of the impeller , the gap (G) between the outer edge of the impeller and the inner lining is maintained and is substantially constant. a width (CW) of each of the cells within the cylindrical portion as measured around a circumference of the cylindrical portion is less than 2 mm, and the impeller is configured to be stabilized with respect to the frame , such that, during rotation of the impeller , the gap (G) between the outer edge of the impeller and the inner lining is maintained and is substantially constant. <EOS>