Blend refrigerants combing hydrofluorocarbons and hydrocarbons are good substitutes to decrease the flammability of hydrocarbons while reducing the global warming potential of hydrofluorocarbons. Four hydrofluorocarbon/hydrocarbon blends (R134a/R290, R134a/R600, R134a/R600a, and R134a/R1270) with various compositions are investigated in vapor-compression heat pump cycles. The effects of hydrocarbon fraction on the blend properties, including critical temperature, critical pressure, latent heat, saturated liquid line, and azeotropic behavior, are comparatively analyzed. Thermodynamic models are established for heat pump simulation. For each R134a/hydrocarbon blend, both the cooling and heating coefficient of performances generally first decrease and then increase with the hydrocarbon mass fraction. The coefficient of performances of R134a/R600 and R134a/R600a have dramatic changes within the hydrocarbon mass fraction of 0.2-1.0, while those of R134a/R290 and R134a/R1270 have dramatic changes within the fraction of 0.0-0.4. Lower condensing or higher evaporating temperatures lead to higher coefficient of performances. In addition, the volumetric capacities first increase and then decrease with the increase of hydrocarbon fraction. R134a/R290 and R134a/R1270 show much higher volumetric capacities as compared to R134a/R600 and R134a/R600a under higher hydrocarbon fractions, which can greatly reduce the required compressor size of pure R134a. The discharge temperatures are kept in the range of 43.0 degrees C-72.3 degrees C for all the blends. To obtain low global warming potential R134a/hydrocarbon blends, the hydrocarbon fraction need to be greater than 0.9, at which R134a/R 1270 performs the best, with cooling/heating coefficient of performances of 5.25/4.70 and cooling/heating volumetric capacities of 4.78/3.53 MJ/m(3). Generally, R134a/R290 and R134a/R1270 perform much better than R134a/R600 and R134a/R600a at the low global warming potential composition. This study can contribute to the determination of hydrofluorocarbon/hydrocarbon compositions based on comprehensive considerations of cycle efficiency, volumetric capacity, and low global warming potential target.