Microcalarimetry is a powerful tool in many research fields; it has been widely utilized to investigate the processes inducing change in the thermodynamic properties of the sample and, thus, it has played an important role in the study of the liquid state, especially in gaining more information on solute-solute interaction in liquid mixtures. — We report here recent measurements on AOT-n-heptane-water micelles performed by means of a new microcalorimeter for liquid samples, from which the apparent molar heat capacity of water confined in the reverse micelle core versus n = [H2O]/[AOT] has been investigated at 25°C.