There are a number of technical devices and apparatus in which in the process of operation the heat received and the heat sink change places. An example is the side surface of a satellite, which periodically serves for receiving the sun heat or its rejecting into the surrounding space. In this connection there arises the necessity to create a reversible device capable of transferring heat under periodic changes of the direction of a heat flow. Ordinary heat pipes possess such a quality, however, the dependence on the orientation at 1-g conditions and a comparatively low heat-transfer capacity restrict their possibilities. Loop Heat Pipes (LHPs) have considerably higher heat-transfer characteristics and are adaptable to different operating conditions, but they are thermal diodes. As a consequence a topical problem is the creation of a reversible loop heat pipe (RLHP) capable of transferring heat in both directions. An ammonia RLHP 2 m long has been created and tested. It demonstrated a maximum capacity of 900 W with heat transferred in both directions and a thermal resistance of 0.035 K/W at a nominal load of 400 W Tests were conducted both in conditions of ordinary environment and in a vacuum chamber.