The invention relates to an impeller (1) of a centrifugal pump apparatus, in particular of a blood pump apparatus, comprising a discoidal body (1) rotatable around an axis (2) of rotation, the body (1) comprising an upper surface (3), a lower surface (4), a central channel (5) extending in the direction of the axis (2) of rotation between the upper and lower surface (3, 4) for guiding fluid, in particular blood through the body (1) in axial direction when the body (1) is rotated in a pump chamber of a pump and several blades (6) supported by the upper surface (3) for pumping fluid, in particular blood, when the body (1) is rotated in a pump chamber of a pump, several spiral grooves (7) in the lower surface (4), each groove (7) having a bottom (7a) and two sidewalls (7b, 7c) and being open in an axial direction, merging into a circumferential surface (8) of the body (1) and extending from this circumferential surface (8) to the central channel (5) at least for providing a pumping action of fluid, in particular blood, from the circumferential surface (8) to the central channel (5) when the body (1) is rotated within a pump chamber of a pump, permanent magnets (10) integrated in the body (1) for driving the impeller by means of a magnetic field wherein each groove (7) is also merging into the central channel (5), one of the sidewalls (7b) of each groove (7) being higher above the bottom (7a) than the other sidewall (7c), in particular the leading sidewall (7b) with respect to the regular direction (R) of rotation being higher than the trailing sidewall (7c), a respective surface area (9) being disposed between each two neighboring grooves (7) and connecting the leading sidewall and the trailing sidewall of neighboring grooves, in particular thus forming a tilted pad area between each pair of neighboring grooves. The invention furthermore relates to a centrifugal blood pump apparatus comprising such an impeller.
