A. Representative surface (red) and intracardiac atrial (green) ECGs (mV) in WT (top) and Zfhx3 KO mice (bottom) after rapid atrial pacing (cycle length of 25 ms). B. Percentage of mice with inducible AA/AF (6/15 WT, 4/6 Zfhx3 Het, and 13/17 Zfhx3 KO mice). C. Comparison of arrhythmia burden by genotype (n = 15 WT, 6 Zfhx3 Het, and 17 Zfhx3 KO mice). D. Frequency of AA/AF in each group at 3-months-old (n = 15 WT, 6 Zfhx3 Het, and 17 Zfhx3 KO mice). E. Representative surface (red) and intracardiac atrial (green) ECGs (mV) in Zfhx3 KO mice showing atrial tachycardia termination and resumption. Time between beats indicated in ms. AA indicates atrial arrhythmia; AF, atrial fibrillation; ECGs, electrocardiogram; AT, atrial tachycardia, NSR, normal sinus rhythm. Data are mean ± s.e.m. P values indicated. Significance of arrhythmia induction and frequency of AA/AF were determined with Mann-Whitney test.