The invention relates to a fluid pump, in particular to a liquid pump having a rotor (18) with at least one rotor blade (20, 21) for conveying the fluid, the rotor being variable with respect to its diameter between a first, compressed state and a second expanded state. In order to produce simple compressibility and expandibility of the rotor of the pump, it is provided according to the invention that at least one rotor blade is deformable between a first state which it assumes in the compressed state of the rotor and a second state which it assumes in the expanded state of the rotor by means of a fluid counterpressure (23) during a rotation of the rotor during pump operation.