An impeller and rotor structure for a magnetically levitated pump define a smooth primary flow path and U-shaped secondary flow path, which extends around an annular magnetic rotor. The u-shaped secondary flow path is defined by a large outer side gap along an outer surface of the rotor, a large bottom gap along a bottom surface of the rotor and a large inner gap along an inner surface of the rotor. Shroudless impeller blades are purely radial and overhung from a thin peripheral ring attached to the annular magnetic rotor. A center post having a low aspect ratio extends through the annular rotor. The low aspect ratio is configured to prevent flow in the primary flow path from colliding directly with flow in the secondary flow path at the inner radial gap.
