  The feasibility of using lattice chiral fermions which are free of $O(a)$
errors for both the heavy and light quarks is examined. The fact that the
effective quark propagators in these fermions have the same form as that in the
continuum with the quark mass being only an additive parameter to a chirally
symmetric antihermitian Dirac operator is highlighted. This implies that there
is no distinction between the heavy and light quarks and no mass dependent
tuning of the action or operators as long as the discretization error $O(m^2
a^2)$ is negligible. Using the overlap fermion, we find that the $O(m^2a^2)$
(and $O(ma^2)$) errors in the dispersion relations of the pseudoscalar and
vector mesons and the renormalization of the axial-vector current and scalar
density are small. This suggests that the applicable range of $ma$ may be
extended to $\sim 0.56$ with only 5% error, which is a factor of $\sim 2.4$
larger than that of the improved Wilson action. We show that the generalized
Gell-Mann-Oakes-Renner relation with unequal masses can be utilized to
determine the finite $ma$ errors in the renormalization of the matrix elements
for the heavy-light decay constants and semileptonic decay constants of the B/D
meson.
