In many engineering problems involving adiabatic (dynamic) conditions the temperature rise induced by plastic deformation is usually evaluated using the inelastic heat fraction. The latter is still frequently considered as a crudely determined constant value. On the other hand, experimental investigations have shown that the inelastic heat fraction depends on strain, strain rate and temperature. Employing a phenomenological double-potential, elastic/thermoviscoplastic constitutive framework, the intrinsic dissipation form and heat equation considered correspond to salient features of inelastic behaviour of a large class of solids. For some typical strain hardening/softening and thermal softening combinations encountered, the evolution of inelastic heat fraction is being studied and quantified and finally shown to be highly strain and temperature dependent.