  We perform a study of the $B^{(*)}$, $D^{(*)}$ semileptonic decays, using a
different method than in conventional approaches, where the matrix elements of
the weak operators are evaluated and a detailed spin-angular momentum algebra
is performed to obtain very simple expressions at the end for the different
decay modes. Using only one experimental decay rate in the $B$ or $D$ sectors,
the rates for the rest of decay modes are predicted and they are in good
agreement with experiment. Some discrepancies are observed in the $\tau$ decay
mode for which we find an explanation. We perform evaluations for $B^*$ and
$D^*$ decay rates that can be used in future measurements, now possible in the
LHCb collaboration.
