  Explicit relations between the isospin mixing probability, the spreading
width $\Gamma_{IAS}^{\downarrow}$ of the Isobaric Analog State (IAS) and the
statistical decay width $\Gamma_c$ of the compound nucleus at finite excitation
energy, are derived by using the Feshbach projection formalism. The temperature
dependence of the isospin mixing probability is discussed quantitatively for
the first time by using the values of $\Gamma_{IAS}^{\downarrow}$ and of
$\Gamma_c$ calculated by means of microscopic models. It is shown that the
mixing probability remains essentially constant up to a temperature of the
order of 1 MeV and then decreases to about 1/4 of its zero temperature value,
at higher temperature than $\approx$ 3 MeV, due to the short decay time of the
compound system.
