Co-culture of H9c2 and stem cells in normal conditions. (A) Cardiomyoblasts (green) and MSCs (red) after one day co-cultivation. (B) A representative double labeled cell with double nuclei (nuclei were stained with Hoechst). (C) DiO-labeled cardiomyoblasts (green) and DiD-labeled MSCs (red) analyzed with flow cytometry after one day co-cultivation. We found three different cell populations: 59.42% of DiO-labeled H9c2 cells, 30.1% of DiD-labeled MSCs and 8.14% of double labeled cells. (D) The distribution according to the forward scatter plot demonstrates that several double labeled yellow cells are mostly the same size as the green H9c2 cells or the red MSCs disapproving complete cell fusion.