Platelet MEKK3 deficiency reduced microvascular obstruction and infarct expansion post-MI. (A) CD42C staining of hearts from MEKK3^f/f and MEKK3^−/− mice on day 3 following ligation of the LAD artery (original magnification ×400). Relative platelet (plt) number (pixels) in 4 random fields per experiment was quantified (mean ± SD). (B) Masson’s trichrome staining in parasternal short-axis sections of hearts from MEKK3^f/f and MEKK3^−/− mice on day 7 post-LAD coronary artery ligation (original magnification ×20). Masson’s trichrome–stained areas were measured. Infarct size is expressed as a percentage of the LV area (n = 3, mean ± SD). (C) Representative M-mode echocardiograms for MEKK3^f/f and MEKK3^−/− mice on day 7 post–LAD coronary artery ligation. (D) Echocardiography quantification of LVEF, LVFS, LVESV, LVEDV, LVIDs, and LVIDd in MEKK3^f/f and MEKK3^−/− mice on day 7 post–LAD coronary artery ligation (n = 8-10, mean ± SD). *P < .05, **P < .01, ***P < .001. IVS, interventricular septum; PW, posterior wall.