In the present study, we conducted a thorough characterisation of the atria and atrial myocytes from two cardiomyocyte-specific transgenic mouse models: IGF1R Tg mice which display ventricular hypertrophy accompanied by enhanced systolic ventricular function, no evidence of arrhythmia, and enlarged atria [12,16], and DCM-dnPI3K Tg mice which display ventricular dilatation, reduced systolic ventricular function, arrhythmia including intermittent AF, enlarged atria and lung congestion [15,16]. The gene discussed is IGF1R; the disease is Arrhythmia.