A major issue related to the performance of sliding pendulum isolators employed for the seismic protection of building and structures concerns the heat generation occurring at the sliding interface under large friction forces and high velocities, and the effects of temperature rise on the properties of the friction materials. In this contribution the problem is approached by studying the heat state of seismic isolation units using computer analyses. A finite element model of the pendulum unit was developed and movement at constant speed is applied between the friction surfaces. The generation of frictional heat is reproduced by a heat source located between the two moving parts, with intensity calculated based upon friction coefficient, contact pressure and velocity. Experiments carried out on real scale isolators confirm the reliability of model predictions. The procedure can be a useful design tool for carrying out computational investigations within a wide range of loading and material parameters