Abstract Energy dissipation is investigated for reactions induced by intermediate energy heavy ions. The simplest situation concerns peripheral collisions for which one discusses the percistency of deep inelastic processes. The mechanism for energy deposit is analysed. Central collisions lead to much larger dissipation. The influence of the bombarding energy of the symmetry of the system is discussed. Then the nature of the dissipated energy is investigated: what is the role of the time derivative of the deposited energy? In other words, what is the role of dynamical effects such as compression? Experiments devoted to flow analysis or to multifragmentation will give the key of this question.