In an absorption heat pump, the separation of the miscible mixture is a great energy consumer, which significantly limits the COP of the system. We propose a new heat pump concept in which the working fluid is a partially miscible mixture. These solutions exhibit very dissymetric properties depending on the pressure level: Under low pressure and temperature, the mixture is composed of two immiscible phases in thermodynamic equilibrium. Then any solution spontaneously splits into these two liquid phases by simple decantation without any energy supply. This phenomena is called demixtion. Another important fact is that the degree of miscibility increases with the pressure and so, beyond a critical pressure of dissolution the two earlier immiscible phases become completely miscible and form an homogeneous liquid phase. In this condition, at high temperature, the volatile phase is evaporated and its vapor is absorbed in the non-volatile phase, exactly in the same process and equipment as in the case of a classical absorption heat pump. For this new process, the COP is 100 to 200 times higher than that for the conventional heat pump.