A blood pump intended to be carried by a freely moving patient uses perpendicular magnetic and electrical fields to propel blood. A rod mounted coaxially inside a tube has electrodes in blood contact for establishing a radial electric field, and an inductor having windings parallel to the axis of the tube is used to establish a circumferential magnetic field. To avoid the evolution of gas at the electrode surfaces the magnetic and electric fields are periodically reversed, and the electrodes are made to have very high surface areas. The blood pump is powered by batteries or fuel cells (or a combination of both) to provide long service between recharging and to reduce the weight carried by the patient.