  After improving the knowledge about residua of the semileptonic form factor
at its first two poles we show that $f_+^{D\pi}(q^2)$ is not saturated when
compared with the experimental data. To fill the difference we approximate the
rest of discontinuity by an effective pole and show that the data can be
described very well with the position of the effective pole larger than the
next excitation in the spectrum of $D^\ast$ state. The results of fits with
experimental data also suggest the validity of superconvergence which in the
pole models translates to a vanishing of the sum of residua of the form factor
at all poles. A similar discussion in the case of $B\to \pi \ell\nu_\ell$ leads
to the possibility of extracting $\vert V_{ub}\vert$, the error of which
appears to be dominated by $g_{B^\ast B\pi}$, which can be nowadays computed on
the lattice. In evaluating the residua of the form factors at their nearest
pole we needed the vector meson decay constants $f_{D^\ast}$ and $f_{B^\ast}$,
which we computed by using the numerical simulations of QCD on the lattice with
$N_{\rm f}=2$ dynamical quarks. We obtain, $f_{D^\ast}/f_D=1.208(27)$ and
$f_{B^\ast}/f_B=1.051(17)$.
