Heparin-produced cerebral hemorrhage. (A) Representative photographs of cerebral sections (1 mm) from heparin-treated WT and tPA KO mice. At 48 hours after MCA occlusion, gross cerebral hemorrhage was observed only in WT mice with heparin administration. Scale bars equal 5 mm. (B) Photomicrograph of cerebral hemorrhage from WT mice. Inset is 1.7-fold magnified from the area denoted by the asterisk. Scale bar equals 2 mm. (C) Effect of heparin on hemorrhage volume. Infusion of heparin 3 hours after MCAO significantly increased hemorrhage volume in WT mice but not in tPA KO mice. (D) No significant differences in infarct volumes were observed among any of the groups (n = 6). (C-D) Values are means ± SD. ^**P < .01.