  We analyze the decay of classically chaotic quantum systems in the presence
of fast ballistic escape routes on the Ehrenfest time scale. For a continuous
excitation process, the form factor of the decay cross section deviates from
the universal random-matrix result on the Heisenberg time scale, i.e. for times
much larger than the time for ballistic escape. We derive an exact analytical
description and compare our results with numerical simulations for a dynamical
model.
