NGF and atrial fibrillation: Under the 8 hours/16 hours/8 hours/16 hours stretch protocol (Figure 4), gene expression analysis revealed significant upregulation of TLR2 (1.91- ± 0.20-fold and 1.81 ± 0.02-fold, respectively; P = 0.002 and P = 0.004, respectively), TLR4 (2.03- ± 0.10-fold and 1.35- ± 0.10-fold; P = 0.002 and P = 0.01, respectively) and NGF (1.40- ± 0.15-fold and 1.61- ± 0.02-fold; P = 0.008 and P = 0.0012, respectively) in both NP and AF cells, respectively, compared to static controls (Figure 4B).