  The world-line formalism is used for the evaluation of the mixed
heavy-quark-gluon condensate in two models of QCD - the stochastic vacuum model
and the dual superconductor one. Calculations are performed for an arbitrary
dimensionality of space-time $d\ge 2$. While in the stochastic vacuum model,
the condensate is UV finite up to $d=8$, in the dual superconductor model it is
UV divergent at any $d\ge 2$. A regularization of this divergence is proposed,
which makes quantitative the condition of the type-II dual superconductor. The
obtained results are generalized to the case of finite temperatures.
Corrections to the both, mixed and standard, heavy-quark condensates, which
appear due to the variation of the gauge field at the scale of the vacuum
correlation length, are evaluated within the stochastic vacuum model. These
corrections diminish the absolute values of the condensates, as well as the
ratio of the mixed condensate to the standard one.
