Chiral perturbation theory for hadrons containing a heavy quark

An effective Lagrangian that describes the low-momentum interactions of mesons containing a heavy quark with the pseudo Goldstone bosons $\ensuremath{\pi}$, $K$, and $\ensuremath{\eta}$ is constructed. It is invariant under both heavy-quark spin symmetry and chiral ${\mathrm{SU}(3)}_{L}\ifmmode\times\else\texttimes\fi{}{\mathrm{SU}(3)}_{R}$ symmetry. Implications for semileptonic $B$ and $D$ decays are discussed.