Massive variable main sequence stars have frequency spectra dominated by acoustic modes excited by the κ mechanism at work in layers where partial ionization of iron group elements produce a peak in opacity. In addition the most advanced of these stars present mixed modes i.e. modes with a g-character in deep layers and p-character in the envelope. Hydrogen burning takes place in a convective core surrounded by a region of varying chemical composition and an envelope mostly radiative except for tiny convective layers related to partial ionization of helium and/or iron group elements. As in lower mass stars the extent of the fully or partially mixed region located just above the convective core "(extra-mixed zone)" is one of the main uncertainties affecting theoretical modeling.