An intravascular blood pump (1) comprises a pump casing (2) having a blood flow inlet (21) and a blood flow outlet (22), and an impeller (3) arranged in said pump casing (2) so as to be rotatable about an axis of rotation, wherein the impeller (3) has blades (31) sized and shaped for conveying blood from the blood flow inlet (21) to the blood flow outlet (22). The blood pump (1) further comprises a drive unit (104) for rotating the impeller (3), the drive unit (104) comprising a plurality of posts (140) arranged about the axis of rotation (10). Coil windings (47) around the posts are sequentially controllable so as to create a rotating magnetic field. The shaft portion (141) of each of the posts (140) comprises a soft magnetic material which is discontinuous in cross-section transverse to the longitudinal axis of the respective post (140).