We study a relation between the spreading width of the isobaric analog
state and the isospin mixing probability of the corresponding parent
state by using the Feshbach projection method. The formula is applied
for calculations of the spreading width of several heavy isotopes and
compared with available experimental data. Contributions from isovecto
r monopole states are found to be important to explain quantitatively
the experimental spreading width. The isospin dependence of the calcul
ated width of several isotopes is also found to be consistent with the
experimental observations.