  We analyze the inclusive $b(c) \to s(u) \mu^+ \mu^-$ and the exclusive
$B(D^+) \to K(\pi^+) \mu^+ \mu^-$ flavour changing neutral current decays in
the light of HyperCP boson $X^0$ of mass 214 MeV recently observed in the
hyperon decay $\Sigma^+ \to p \mu^+ \mu^-$. Using the branching ratio data of
the above inclusive and exclusive decays, we obtain constraints on $g_1 (h_1)$
and $g_2 (h_2)$, the scalar and pseudo-scalar coupling constants of the
$b-s-X^0 (c-u-X^0)$ vertices.
