  We describe a new efficient mechanism of reheating. Immediately after rolling
down the rapidly moving inflaton field $\phi$ produces particles $\chi$, which
may be either bosons or fermions. This is a nonperturbative process which
occurs almost instantly; no oscillations or parametric resonance is required.
The effective masses of the $\chi$ particles may be very small at the moment
when they are produced, but they ``fatten'' when the field $\phi$ increases.
When the particles $\chi$ become sufficiently heavy, they rapidly decay to
other, lighter particles. This leads to an almost instantaneous reheating
accompanied by the production of particles with masses which may be as large as
$10^{17}-10^{18}$ GeV. This mechanism works in the usual inflationary models
where $V(\phi)$ has a minimum, where it takes only a half of a single
oscillation of the inflaton field $\phi$, but it is especially efficient in
models with effective potentials slowly decreasing at large $\phi$ as in the
theory of quintessence.
