  This paper studies the stability of warm inflationary solutions when the
viscous pressure is taken into account. The latter is a very natural and
physically motivated ingredient of warm inflation and is seen to widen the
stability range of warm inflation. The spectral index parameters, $n_{s}$,
$n_{T}$, and their ratio are derived. The corresponding WMAP7 data are used to
fix some parameters of the model. Two specific examples are discussed in
detail: (i) a potential given by $V(\phi, T) = v_{1}(\phi)\, + \, v_{2}(T)$,
and (ii) a potential of the form $V(\phi, T) = \alpha \, v_{1}(\phi) \,
v_{2}(T)$. In both cases, the viscosity has little impact on the said ratio.
