While Papadatos et al. reported that heterozygous Scn5a+/- mice with 50% decrease in the Nav1.5 gene and protein expression did not exhibit any obvious abnormalities or difference in heart weight compared to Wt mice but presented with a prolongation of P wave and PR interval with no change in QTc or AV block [52]. The gene discussed is SCN5A; the disease is atrioventricular block.