Specific heat capacities at constant volume (C-v) were measured with an adiabatic calorimeter for pure pentafluoroethane (R125) and an azeotrope-like mixture of R32 and R125 (R410A) with a mole fraction composition of 0.6975 difluoromethane + 0.3025 pentafluoroethane. Temperatures ranged from 300 K to 400 K, and pressures ranged from 3 MPa to 20 MPa. Measurements were conducted on single-phase liquid and compressed gaseous samples along isochores. Density was reported during each calorimetric experiment. The R410A mixture was gravimetrically prepared from high-purity substances. The principal sources of uncertainty are the temperature-rise measurement and the change-of-volume work adjustment. The expanded relative uncertainty (with a coverage factor k = 2 and thus a 2 SD estimate) for CV is estimated to be 2 % for liquid-phase results, increasing to 4 % for gas results (below critical density). The expanded relative uncertainty for density is 0.2 %.