We next examined the effect of SS-AF-MSC-CM on the proliferation of UCB ECFC derived cells and showed that the presence of MMP-9 inhibitor in SS-AF-MSC-CM resulted in a statistically significant decrease in the proliferation of UCB ECFC derived cells (52.7±7.7%, p<0.05, Student’s t-test, Figure 7b). Here, MMP9 is linked to atrial fibrillation.