A working fluid for a heat cycle containing at least 90 mass % of 1,1,2,2-
tetrafluoroethyl-2,2,2-trifluoroethyl ether (HFE-347) and a C.sub.1-4
alcohol is provided. A Rankine cycle system, a heat pump cycle system and
a refrigeration cycle system using the working fluid for a heat cycle of
the present invention is also provided.