Reconstitution of Sca-1 KO mice with WT BM Sca-1+ cells restored cardiac function after MI. Sca-1 knock-out (KO) mice were reconstituted with wild type (WT) bone marrow (BM) Sca-1+ cells (2×106, (Sca-1+)-KO) for 3 months, then underwent myocardial infarction (MI). Cardiac function was measured by echocardiography at baseline (before MI), 7, 14, 21, and 28 days after MI in WT, Sca-1 KO and (Sca-1+)-KO groups. (A) Representative M-mode echocardiographic images. (B) Fractional shortening. (C) Left ventricular internal end systolic dimension (LVIDs). (D) Left ventricular internal end-diastolic dimension (LVIDd). (E) Eject fraction (EF). (F) Representative images of whole sectioned hearts; H&E and Masson's Trichrome staining in WT, Sca-1 KO and (Sca-1+)-KO groups at 28 days after MI. (G) Viable myocardium (identified as red with Trichrome's staining) in the ischemia zone was quantified and expressed as a percentage of the total infarcted area. (H) Scar size thickness is presented as an average of wall thickness measurements taken at the middle and at each edge of the scar area at its thinnest point. (B-E), n=5/group; (G-H), n=6/group; mean ± SD; * vs. WT, P<0.01; # vs. KO, P<0.05.