  In this talk, we describe part of a recent work on the correlation function
of a V-A current with a V+A current in the framework of QCD in the limit of a
large number of colours Nc. The discussion takes place within two successive
approximations of this theory, called MHA and MHA+V'. Results concerning the
evaluation of chiral condensates of dimension six and eight, as well as matrix
elements of the Q7 and Q8 electroweak penguin operators, are given.
