A previous study reported sinus bradycardia with unaltered contractile properties in isolated heart from Cav1.3−/− mice38 suggesting that while Cav1.2 is the only L-type Ca2+ channel isoform involved in heart contractility, Cav1.3 plays a major role in heart automaticity and conduction. The gene discussed is CACNA1D; the disease is Sinus bradycardia.