MEIS1 and sick sinus syndrome: In Fosl-2tg hearts, we observed lower transcripts levels of genes involved in: the regulation of cardiac rhythmicity (Meis1, Nfia), the functional development, maturation, and homeostasis of the conduction system (Tbx3), higher resting HR, atrial fibrillation and left ventricular mass (Sox5), long QT syndrome (Scn10a, Kcnq1), Brugada syndrome, sick sinus syndrome, and atrial fibrillation (Scn10a, Nos1ap) (Fig. 3e).