Identification and characterization of PKH26+ (fluorescent) labeled donor cells in damaged myocardium 3 weeks following direct injection of Bone Marrow Mononuclear cells (BMMCs) into myocardium. A) Overlay of PKH26 fluorescence (red) on 160× bright field image of unfixed cryostat section reveals bright red foci, which represent engrafted PKH26+ donor BMMCs. B) Overlay of beta cardiac myosin heavy chain immunofluoresence (IF = green) with PHK26 fluoresence (red) and Hoesch 33258 fluoresence (blue) reveals red donor cells at the interface between scar (left) and myocardium (right). Yellow MyHC+/PKH26 + BMMCs derived cardiomyocytes can also be observed. (Mag 160×).