  We evaluate the two-loop QCD diagrams contributing to the leading color
coefficient of the heavy-quark pair production cross section in the gluon
fusion channel. We obtain an analytic expression, which is valid for any value
of the Mandelstam invariants s and t and of the heavy-quark mass m. Our
findings agree with previous analytic results in the small-mass limit and with
recent results for the coefficients of the IR poles.
