The loss of cardiomyocytes by apoptosis and the subsequent replacement by fibrous connective tissues are important features of cardiac remodeling in adult heart disease. In children with CHD, however, the cellular and molecular mechanisms of heart failure have not yet been fully understood because of the anatomical and hemodynamic complexities. To investigate the apoptotic death of cardiomyocytes and mobilization of cardiac progenitor cells in children with congenital heart disease (CHD), terminal deoxynucleotidyl-transferase-mediated dUTP nick end-labeling (TUNEL) assay and immunohistochemistry with antibody against c-kit were performed. The incidence of TUNEL-positive cardiomyocytes in children with CHD (n=17) was higher (0.39+/-0.21%) than that in the child controls (0.072+/-0.037%, p<0.001, n=6), however, the incidence was lower than that in adults with heart disease (1.35+/-0.54%, p<0.005, n=7). Significant cardiomyocyte hypertrophy or fibrosis was not observed in children with CHD. The CHD patients hemodynamically demonstrating a volume overload showed more TUNEL-positive cardiomyocytes (0.58+/-0.17%, n=4) than those with severe cyanosis (0.20+/-0.12%, p<0.05, n=4). C-kit-positive cells were more abundantly detected in CHD in comparison to the child control (p<0.01) and the adults with heart disease (p<0.005). The incidence of c-kit-positive cells correlated with that of TUNEL-positive cardiomyocytes (r=0.513). In contrast to adult patients with heart disease where cardiomyocyte apoptosis and the subsequent replacement by fibrous connective tissue are characteristic features of remodeling process, stress in children with CHD was found to induce less cardiomyocyte apoptosis and fibrosis. This study also provides a possible relationship between cardiomyocyte apoptosis and mobilization of c-kit-positive cells in children with CHD.