  The SU(3) breaking effects due to light quark masses on heavy meson masses,
decay constants ($F_{D}, F_{D_{s}}$) and the form factor for semileptonic
$\overline{B}\rightarrow D^{(\ast)} l\bar{\nu}_{l}$ transitions are formulated
in chiral perturbation theory, using a heavy meson effective Lagrangian and
expanding in inverse powers of the heavy meson mass. To leading order in this
expansion, the leading chiral logarithms and the required counterterms are
determined. At this level, a non-analytic correction to the mass splittings of
${\cal O}(p^3)$ appears, similar the the one found in light baryons. The
correction to $F_{D_{s}}/F_{D}$ is roughly estimated to be of the order of
$10\%$ and, therefore, experimentally accessible, while the correction to the
form factor is likely to be substantially smaller. We explicitly check that the
heavy quark symmetry is preserved by the chiral loops.
