Abstract: A heat engine utilizing a cycle having an isenthalpic pressure-increasing phase wherein, in the entropy-reduction phase of the cycle for changing the state of the working fluid, in order to have at least a part of that phase change at constant enthalpy, a compensating fluid (high-pressure feed) at a pressure higher than that of the cycle working fluid is introduced into the cycle system at the beginning of the isenthalpic change, thus increasing the pressure of the working fluid, and then the entropy of the working fluid is reduced by discharging a part of the working fluid to the outside of the cycle system at the end of the isenthalpic change.