SCN5A and long QT syndrome 3: Whilst showing prolonged electrocardiographic QT and QTc intervals expected for LQT3, Scn5a+/Δ mice showed frequent episodes of sinus bradycardia, sinus pause/arrest, and increased sinus node recovery times, suggesting compromised pacemaker activity, as well as depressed intra-atrial, atrioventricular node, and intraventricular conduction.