of the rotor has a radial configuration in fig2 a an embodiment with axial inflow and outflow is represented schematically the rotor has a rotor blade carrier 19 and also rotor blades 20 21 the rotor blades 20 21 being folded out during pump operation i e in the expanded state of the rotor the radius of the rotor during operation is coordinated to the internal diameter of the pump housing in the expanded state thereof if the pump head is intended to be removed from the heart 1 then the pump operation is ceased and the rotor blades 20 21 abut against the rotor blade carrier 19 in order to reduce the radius of the rotor 18 this is advantageously assisted by rotation of the rotor 18 in the direction of rotation opposite to the pump operation if the shaft 16 is then displaced towards the pump head 3 in the manner of a bowden cable then the pump head again assumes its compressed form and can be removed through the blood vessel 12 fig3 shows in detail a plan view on the rotor 18 with the rotor blade carrier 19 and the rotor blades 20 21 these being represented in a continuous shape in their first state i e the compressed state of the rotor the rotor blades can also abut even more closely against the rotor blade carrier 19 in the first state it is important that when the pump operation and rotation of the rotor 18 starts in the direction of rotation 22 required for the conveyance operation a fluid counterpressure is produced in the direction of the arrow 23.