Abstract: The invention relates to a heating cycle system of a motor vehicle which includes the vehicle internal combustion engine, a heating device which is independent of the engine, an interior heat exchanger, a circulating pump, and a bypass line which connects a return line to a flow line. According to the invention the circulating pump is driven by a reversible electric motor and is used as a control element for selective operation of a small cycle including only the heating device and the vehicle heat exchanger or a large cycle which also includes the internal combustion engine. The direction of operation of the circulating pump controls a valve which directs fluid to either the small or the large cycle.