  Thermodynamics of a heavy quark-antiquark pair in SU(3)-QCD is studied below
the deconfinement critical temperature, $T_c$. In the quenched case, a model of
the string passing through heavy valence gluons yields a correct estimate of
$T_c$ and a behavior of the string tension near $T_c$. For two light flavors,
entropy and internal energy can be obtained from the partition function of
heavy-light mesons and baryons. They are in a good qualitative agreement with
the lattice results.
