Performance analysis of totally irreversible heat pumps and refrigerators has been developed by means of the second law of thermodynamics. The machine operates steadily between two variable temperature heat reservoirs. The results show that the optimal balance between the sizes of the heat exchangers at the hot and cold ends of the machine is affected by the ratio E (or E'). Also, the heat delivered by the heat pump and the heat removed by the refrigerator varies significantly with E (or E'). Conversely, the coefficient of perfonnance does not depend on E (or E'). Finally, the effect of the internal irreversibility diminishes at E-h/E-c < 1, for heat pumps and at E-h/E-c > 1, for refrigerators.