A heart pump including a housing defining a cavity including at least one inlet and at least one outlet, an impeller provided within the cavity, the impeller including vanes for urging fluid from the inlet to the outlet upon rotation of the impeller, a drive that rotates the impeller within the cavity, a magnetic bearing including at least one bearing coil that controls an axial position of the impeller within the cavity, a sensor that senses an axial position of the impeller within the cavity and a controller. The controller includes an electronic processing device that, in response to a change in axial hydraulic forces on the impeller determines an axial position of the impeller within the cavity, determines a reference power in accordance with the determined axial position and controls the magnetic bearing to cause the impeller to move until a bearing power indicator indicative of the power used by the magnetic bearing reaches the reference power.
