Form Factors for $B\to\pi$ and $D\to\pi$ Transitions
  Armed with the information on the form factor $\fdpi(0)$ inferred from recent CLEO measurements of SU(3)-breaking effects in charmed meson decays, we have studied the form factor $\fbpi$. In the heavy quark limit, $\fbpi(q^2)$ is related to $\fdpi(q^2)$ in the kinematic region close to zero recoil. Assuming pole dominance for its $q^2$ dependence, $\fbpi(0)$ is estimated to be $\approx 0.39\,.$ If the requirement of heavy quark symmetry is relaxed so that it applies only to soft pion emissions from the heavy meson, we find that $\fbpi(0)$ is more likely of order $0.55\sim 0.60\,.$ 
Hai-Yang Cheng