  We extend the Fermilab method for heavy quarks to include all interactions of
dimension six in the action. We discuss a subtlety in the power counting, which
implies that, for heavy quarks, certain interactions of dimension seven are
commensurate with some of those of dimension six. We then present tree-level
matching conditions obtained from calculating the Compton scattering amplitude
for (lattice) QCD. When the matching conditions have been applied, the improved
action removes (tree-level) discretization errors of order $a^2\bm{p}^3/m_Q$
and $a^3\bm{p}^3$.
