  We study electron-positron pair creation {from} the Dirac vacuum induced by a
strong and slowly varying electric field (Schwinger effect) which is
superimposed by a weak and rapidly changing electromagnetic field (dynamical
pair creation). In the sub-critical regime where both mechanisms separately are
strongly suppressed, their combined impact yields a pair creation rate which is
{dramatically} enhanced. Intuitively speaking, the strong electric field lowers
the threshold for dynamical particle creation -- or, alternatively, the fast
electromagnetic field generates additional seeds for the Schwinger mechanism.
These findings could be relevant for planned ultra-high intensity lasers.
