  Taking into account the quadratic in mass terms in the effective chiral
lagrangian, we show that, at \theta \sim \pi, the theory with 2 light quarks of
equal mass involves two degenerate vacuum states separated by a barrier. For
three flavors, the energy barrier between two vacua appears already in the
leading order in mass. This corresponds to the first order phase transition at
\theta = \pi. The surface energy density of the domain wall separating two
different vacua is calculated. In the immediate vicinity of the phase
transition point, two minima of the potential still exist, but one of them
becomes metastable. The probability of the false vacuum decay is estimated.
