An automated flow calorimeter has been developed for the measurement of high accurate isobaric heat capacities for pure compounds and mixtures over the range 250-400 K and 0-20 MPa. The technique has been checked for different compounds and at different conditions of temperature and pressure and the results have been compared with the literature values available. The conclusion of this comparison is that the new calorimeter can measure heat capacities with an estimated total uncertainty better than 0.5%. This paper report describes the new equipment, its set-up and gives new heat capacity data for toluene and ethyl tert-butyl ether at different temperatures and pressures. (C) 2008 Elsevier B.V. All rights reserved.