UCB-MNCs transplantation augments myocardial cell proliferation and attenuates myocardial fibrosis. Myocyte proliferation was assessed by Ki-67 immuno-fluorescence staining in RV of (A) PAB-only and (B) UCB-MNCs treated animals. Ki-67 positive cells were stained green and nuclei were in blue. The Ki-67 expressions were quantified and data are shown in a bar graph (C). Cell transplantation of UCB-MNCs results in enhanced cellular proliferations when compared to PAB-only animals (***P–value <0.005 versus PAB; scale bars = 100 μm). The images were representatives of three PAB-only and three cells treated samples. (D) Representative images of control, PAB and UCB-MNCs transplanted RV (n = 5 each) stained for hematoxylin and eosin (H & E) for any lesions or tumor formation. (E) Histological sections were stained with Masson-Trichrome stain (blue) to identify the fibrotic area of RV in response to PAB and cells delivery. Viable myocardial cells was stained red and fibrosis was blue (scale bars = 50 μm). (F) Percentage circumferential fibrosis measured in short-axis Masson-Trichrome staining was significantly smaller in UCB-MNCs transplanted heart compared to the PAB-only group (***P–value <0.005 versus PAB and control). PAB, pulmonary artery banding; RV, right ventricle; UCB-MNCs, umbilical cord blood-mononuclear cells.