While sodium channel (SCN5A) mutant E428K-iPSC-aCMs exhibited a faster beating rate and greater coefficients of variation (based on peak-to-peak interval variability, thereby indicating irregular AF-like beating patterns) in both RM and PC compared to WT-and E428K-GC-iPSC-aCMs, only PC maintained an adult-like (lower) beating rate. This evidence concerns the gene SCN5A and atrial fibrillation.