The effect of two heat additions, rather than one, in a gas turbine engine is analysed using a regenerative Brayton cycle model, where all fluid friction losses in the compressor and turbine are quantified by an isentropic efficiency term and all global irreversibilities in the regenerator are taken into account by means of an effective efficiency. It has been established that the application of an isothermal heat addition process in regenerative gas turbine engines may result in significant efficiency improvements of over 10% compared with conventional engines. Moreover, substantial reductions of pollutant emissions are expected.