Mouse genetic models revealed that partial atrial NCX1 knock out (≈90%) caused severe bradycardia and other rhythm disorders (Herrmann et al., 2013), while complete atrial NCX knock-out completely suppressed the atrial depolarization exerting ventricular escape rhythm on the ECG (Groenke et al., 2013). This evidence concerns the gene TLX2 and Bradycardia.