A thermodynamic machine, comprising: a rotor, configured to rotate about a rotor axis, a working fluid circulation path and a coolant fluid path formed within the rotor, the coolant fluid path fluidically isolated from the working fluid circulation path, the working fluid circulation path spanning radially from the rotor axis to close to the periphery of the rotor; a working fluid circulation drive configured to drive the circulation of a working fluid about the working fluid circulation path; at least one working fluid cooler heat exchanger formed as part of the working fluid circulation path and the coolant fluid path, in use coolant fluid passing through the working fluid cooler heat exchanger to transfer heat from the working fluid to the coolant fluid, and; a working fluid heater in the working fluid circulation path configured to heat a working fluid circulating around the working fluid circulation path.