A. Representative traces of calcium transients recorded from WT (top) and Zfhx3 KO (bottom) mice left atrial cardiomyocytes with fluo-3AM and paced at 1 Hz. Mean amplitude (B, n = 28 WT and 14 Zfhx3 KO cells), time to peak (C, n = 27 WT and 15 Zfhx3 KO cells), and decay time constants (D, n = 27 WT and 15 Zfhx3 KO cells) of calcium transients. E. Representative traces of spontaneous calcium events after 1 min of pacing at 1 Hz. F. Mean spontaneous calcium events per second without pacing (n = 20 WT and 19 Zfhx3 KO cells). Data are mean ± s.e.m. P values are indicated. Groups were compared using unpaired t tests