The transformation of renewable or waste heat into mechanical power by the Organic Rankine Cycle (ORC) has become established as a robust and cost-effective technology. However, it must be considered that these applications normally come with a limited temperature difference between the source and the sink, which is why the maximal achievable thermal efficiency is already low in comparison with conventional power plants. In addition, this Carnot efficiency is not achievable by real ORC systems. The reasons for this are not only irreversible components or the necessary temperature differences for heat absorption or rejection, but also the need of preheating the working fluid, which is an immanent characteristic of the Rankine process itself. Thus, the mean temperature of heat absorption differs from that of a Carnot process, resulting in a limited second law efficiency. This publication describes a novel thermodynamic power cycle with the aim of completely avoiding preheating losses, which is called the Recuperative Two-Phase Power Cycle (PC-RTPC). Regarding the state changes, the process resembles the concept of the Ericsson cycle. Deviating from it, the working fluid undergoes a phase change, which implies significant advantages compared to a process using a gaseous working fluid. This is made possible by a non-linear zeotropic mixture composed of a main and an ancillary working fluid. The key element is an internal heat exchanger, which separates the two temperature levels of the source and the sink, while on its low-pressure side a condensation takes place. The primary technical challenge is an expansion into the two-phase region. For the basic cycle, which is intended to convert latent heat sources, an isothermal expansion is required. For the conversion of the sensible heat source this challenge could be avoided. This work illustrates the concept of such a cycle by a theoretical investigation and an exemplary working fluid selection for a latent heat source of 100 °C. The endoreversible cycle with an isothermal expansion is able to reach a second law efficiency of 85.8% applied to the source and sink temperatures.