A thermoviscous steady shock is studied through its interaction with small-amplitude perturbations introduced far behind the shock region and convected uniformly towards it. It is assumed that a significant broadening of the shock region may be brought about by the amplification of the fluctuations as they pass through it. The scale of such broadening effects, however, is found to depend on the amplitude and frequency of the induced fluctuations. Indeed, well-defined ranges of these parameters determine the scale of the non-uniform part of the mean flow, and thus, of any effects observed inside the shock region. For specific values of these parameters, we observe not only a broadening, but also a deformation of the shock region. These results are confirmed numerically using a pseudospectral scheme.