We consider a wide class of solar models with mixed core.
Most of these models can be excluded as the predicted sound speed profile is
in sharp disagreement with helioseismic constraints. All the remaining models
predict 7Be and/or 7B neutrino fluxes at least as large as those of SSMs.
In conclusion, helioseismology shows that a mixed solar core cannot account for
the neutrino deficit implied by the current solar neutrino experiments.Comment: 6 pages, RevTeX, plus 5 postscript figure