  The most general Lagrangian consistent with chiral, heavy quark, and strong
interaction symmetries to order $1/M$ and to linear order in the SU(3) vector
and axial currents is presented. Two new dimensionful and five dimensionless
couplings arise at this order. The heavy to light flavor changing current is
derived to the same order, giving rise to two additional dimensionful constants
and six dimensionless ones. The dimensionless parameters are shown to be
irrelevant at \ord. The leading nonanalytic heavy quark and chiral symmetry
violating corrections to heavy meson decay constants are computed, and
implications to B decays are discussed; measurements of the experimentally
accessible form factors for $D \to \pi l \nu$ and $B \to \pi l \nu$, along with
knowledge of the $D^* D \pi$ coupling, determine the eight decay constants
$f_D$, $f_{D_s}$, $f_{D^*}$, $f_{D_s^*}$, $f_B$, $ f_{B_s}$, $f_{B^*}$, and
$f_{B_s^*}$, as well as one relation among the $B \to \pi l \nu$ form factors,
to \ord~. The ratio $R_1 = \frac{f_{B_s}}{f_B}/\frac{f_{D_s}}{f_D}$ is
expressed in terms of two dimensionful couplings.
