  We study the D^{+} -> sigma pi^{+}, D^{+} -> rho^0 pi^{+}, B^{-} -> sigma
pi^{-}, B^{-} -> rho^0 pi^{-} and \bar{B}^0 -> rho^{\pm} pi^{\mp} decays in a
valence quark triangle model, incorporating chiral symmetries. We find a good
agreement with recent experimental data for D^{+} -> sigma pi^{+} and for D^{+}
-> rho^0 pi^{+}. We point out that a "long-distance" contribution due to the
axial vector a_1 meson pole, calculated by using chiral symmetry, can be
relevant to explain D^{+}-> rho^0 \pi^{+} and for lowering the ratio
R=Br(\bar{B}^0 -> rho^{\pm} pi^{\mp})/Br(B^{-} -> rho^0 pi^{-}) to be
consistent with its phenomenological determination, within the large
experimental uncertainity.
