In theories with multiple vacua, reheating to a temperature greater than the
height of a barrier can stimulate transitions from a desirable metastable
vacuum to a lower energy state. We discuss the constraints this places on
various theories and demonstrate that in a class of supersymmetric models this
transition does not occur even for arbitrarily high reheating temperature.Comment: 21 pages, 1 figure. Typos corrected and some references adde