A blood pump comprises a pump housing; a plurality of rotors positioned in said housing, each rotor comprising an impeller having a hydrodynamic surface for pumping blood; and a motor including a plurality of magnetic poles carried by each impeller, having motor stators, each including electrically conductive coils located adjacent to or within the housing. At least one of the rotors is adopted to rotate clockwise, and at least one of rotors is adopted to rotate counterclockwise. By this means, stator or stationary blades between the rotors may not be needed.