  We review results of a numerical study of resonant inflaton decay in a wide
range of realistic models and parameters. Wide enough parametric resonance can
withstand the expansion of the Universe, though account for the expansion is
very important for determining precisely how wide it should be. For example,
the effective production of particles with mass ten times that of the inflaton
requires very large values of the resonance parameter $q$, $q > 10^8$. For
these large $q$, the maximal size of produced fluctuations is significantly
suppressed by back reaction, $< X^2 > \sim 10^{-10} M_{Pl}^2$. We discuss some
physical implications of our results.
