Impeller of a centrifugal pump apparatus, in particular of a blood pump apparatus, comprising a discoidal body rotatable around an axis of rotation, the body comprising a. an upper surface b. a lower surface c. a central channel extending in the direction of the axis of rotation between the upper and lower surface (3,4) for guiding fluid, in particular blood through the body in axial direction when the body is rotated in a pump chamber of a pump and d. several blades supported by the upper surface for pumping fluid, in particular blood, when the body is rotated in a pump chamber of a pump e. several spiral grooves in the lower surface, each groove having a bottom and two sidewalls (7b, 7c) and being open in an axial direction, merging into a circumferential surface of the body and extending from this circumferential surface to the central channel at least for providing a pumping action of fluid, in particular blood, from the circumferential surface to the central channel when the body is rotated within a pump chamber of a pump f. permanent magnets integrated in the body for driving the impeller by means of a magnetic field g. and each groove also merging into the central channel h. and a respective surface area being disposed between each two neighboring grooves 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 characterised in that i. one of the sidewalls of each groove is higher above the bottom than the other sidewall, in particular the leading sidewall with respect to the regular direction of rotation being higher than the trailing sidewall j. each surface area is subdivided in circumferential direction into two parts, a first part being adjacent to the higher sidewall of a groove forming a plateau in circumferential direction and a second part, extending between the plateau and a neighboring groove, having a decreasing height towards the neighboring groove in circumferential direction k. the first part and / or the second part of the surface area form a secondary incline a long a spiral line on the lower surface of the impeller body towards the rotor center. a. an upper surface b. a lower surface c. a central channel extending in the direction of the axis of rotation between the upper and lower surface (3,4) for guiding fluid, in particular blood through the body in axial direction when the body is rotated in a pump chamber of a pump and d. several blades supported by the upper surface for pumping fluid, in particular blood, when the body is rotated in a pump chamber of a pump e. several spiral grooves in the lower surface, each groove having a bottom and two sidewalls (7b, 7c) and being open in an axial direction, merging into a circumferential surface of the body and extending from this circumferential surface to the central channel at least for providing a pumping action of fluid, in particular blood, from the circumferential surface to the central channel when the body is rotated within a pump chamber of a pump f. permanent magnets integrated in the body for driving the impeller by means of a magnetic field g. and each groove also merging into the central channel h. and a respective surface area being disposed between each two neighboring grooves 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 characterised in that i. one of the sidewalls of each groove is higher above the bottom than the other sidewall, in particular the leading sidewall with respect to the regular direction of rotation being higher than the trailing sidewall j. each surface area is subdivided in circumferential direction into two parts, a first part being adjacent to the higher sidewall of a groove forming a plateau in circumferential direction and a second part, extending between the plateau and a neighboring groove, having a decreasing height towards the neighboring groove in circumferential direction k. the first part and / or the second part of the surface area form a secondary incline a long a spiral line on the lower surface of the impeller body towards the rotor center.