HBO preconditioning significantly reduced infarction volume and hemorrhage volume. (A) Representative whole brains and brain slices with 2,3,5-triphenyltetrazolium chloride staining of each groups were demonstrated. HBO-PC reduced infarction volume and attenuated hemorrhagic transformation. (B) Bar graphs showing average infarct size calculated in six slices. HBO-PC significantly reduced infarct volume at 24 h after reperfusion compared to htMCAO group. (C) Hemorrhage volume was significantly reduced with HBO-PC. *P> 0.05 vs. htMCAO.