As a continuation of our studies of the excess functions of binary systems containing acetonitrile (1 - x)-amines (x) mixtures, the molar heat capacity, Cp, and excess molar heat capacity, Cp-E, of acetonitrile + diethylamine or sec-butylamine mixtures have been determined as a function of composition at 288.15, 293.15, 298.15 and 303.15 K at atmospheric pressure using a modified 1455 PARR solution calorimeter. The excess heat capacity data are positive for both systems over the whole composition range. The experimental data on the excess molar heat capacity are discussed in terms of the influence of the magnitude of the experimental excess molar enthalpy, HE, over the curve shaped for the experimental CpE data, molecular interactions in the mixtures, isomeric effect of the amines and modeling of CPE data.367913922