AF inducibility, optical mapping and fibrosis quantification in LA of young control (3 months), young MI (3 months), and aged (20 months) rats. (A) Percentage of rats with inducible AF (n = 8–10; Fisher’s exact test). (B) LA activation maps at BCL 100 ms from a control, young MI, and elderly rat. (C) Mean ± SEM LA conduction velocity and APD₅₀ (n = 6–7; two-way ANOVA followed by Bonferroni test; the P-values indicate Bonferroni-corrected differences between groups from data pooled from all BCLs). (D) Dot-plot graphs show mean ± SEM percentage fibrosis in LA. Points represent results from an individual animal (n = 5–6; one-way ANOVA with Dunnett’s test). AF, atrial fibrillation; APD₅₀, action potential duration to 50% repolarization; BCL, basic cycle length; LA, left atrium; MI, myocardial infarction; SR, sinus rhythm.