  We discuss the stability of homonuclear and heteronuclear mixtures of 3He and
4He atoms in the metastable 2^3S_1 state (He*) and predict positions and widths
of Feshbach resonances by using the Asymptotic Bound-state Model (ABM). All
calculations are performed without fit parameters, using \emph{ab-initio}
calculations of molecular potentials. One promising very broad Feshbach
resonance (\Delta B=72.9^{+18.3}_{-19.3} mT) is found that allows for tuning of
the inter-isotope scattering length.
