  We investigate the isospin-violating mixing of the light scalar mesons
a0(980) and f0(980) within the unitarized chiral approach. Isospin-violating
effects are considered to leading order in the quark mass differences and
electromagnetism. In this approach both mesons are generated through
meson-meson dynamics. Our results provide a description of the mixing
phenomenon within a framework consistent with chiral symmetry and unitarity,
where these resonances are not predominantly q q-bar states. Amongst the
possible experimental signals, we discuss observable consequences for the
reaction J/Psi -> phi pi0 eta in detail. In particular we demonstrate that the
effect of a0-f0 mixing is by far the most important isospin-breaking effect in
the resonance region and can indeed be extracted from experiment.
