[en] Dissipative work is used to address some textbook definitions of heat capacity at constant volume C _Vand at constant pressure C _P. It is shown that dissipative work should be accounted for when this topic is presented to the students, so that all C _V (and C _P) definitions are equivalent, instead of imposing unnecessary restrictions on thermodynamic processes. Finally, one simple but illustrative example is given. This work is also relevant from a didactic and pedagogical standpoint, since it helps dispel some misunderstandings related to the concepts outlined herein. (paper)