To confirm p300, but not CBP, is essential for aging‐related fibrosis and AF induction, Cre + p300 (+/−) (Het) mice [Systemic p300 (−/−) homozygotes are prone to embryonic death] was employed (The genotype identification was shown in Supplemental Methods and Figure S5) (Figure 6a). Here, EP300 is linked to atrial fibrillation.