  We construct a realistic field-theoretic model for the structure of a heavy
meson in the heavy quark limit. The model is fully covariant and satisfies
heavy quark symmetry. The Isgur-Wise function, the decay constant, and the
axial vector coupling constant are studied. This model overcomes the
limitations caused by non-covariance of the light-front quark model, and
provides an ideal framework to systematically evaluate the heavy quark symmetry
breaking effects caused by the $1/m_Q$ correction terms in the heavy quark
effective theory of quantum chromodynamics.
