  I consider a model based on a quark--meson interaction Lagrangian. The
transition amplitudes are evaluated by computing diagrams in which heavy and
light mesons are attached to quark loops. The light chiral symmetry relations
and the heavy quark spin-flavour symmetry dictated by the heavy quark effective
theory are implemented. The model allows to compute the decay form factors and
therefore can give predictions for the decay rates, the invariant mass spectra
and the asymmetries.
