A blood pump is temporarily operated at a low rotational speed lying below a design rotational speed. This involves a risk of thrombogenesis since flow detachments may occur at blades of an impeller of the rotary blood pump. For eliminating deposits at said impeller, the rotational speed of said pump is temporarily increased to the design rotational speed. Alternatively, said pump alternately operates at said design rotational speed and a low rotational speed, and this pulsed operation is synchronized with the heart rate.
