2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/192084We analyse the Lorentz structures of weak decay matrix elements bewteen meson states of arbitrary spin. Simplifications arise in the transition amplitudes for a heavy meson decaying into a light one via a Bethe-Salpeter approach which incorporates heavy quark symmetry. Phenomenological consequences on several semileptonic, nonleptonic and FCNC induced decays of heavy flavoured mesons are derived and discussed.20 RevTex pages, Preprint # UTAS-PHYS-94-04High Energy Physics - Phenomenologytext