The disclosure relates to a pump for implantation into a vessel or a heart, with the pump being introduced in a first state into the vessel or heart in order then be functionally changed over to a second state in the vessel or in the heart, having a drive part and a delivery part, where the drive part is not functional in the first state and becomes functional as a result of the changeover to the second state, wherein the drive part has an electric motor, where the electric motor is embodied as a wet rotor, and where, in the first state, the rotor of the electric motor and the stator of the electric motor are arranged so as to be separate from one another, and where the rotor of the electric motor is moved into the stator of the electric motor in the second state, where the rotor can drive the delivery part in the second state.