We looked at the Scn5a gene which codes for a pore forming protein and is mutated in human heart conduction diseases (Online Mendelian Inheritance in Man 601144, 113900) and for which heterozygous mutant mice suffer from abnormal heartbeats and defects in the impulse conduction system and also at Scn10a recently implicated in heart conduction [24]. This evidence concerns the gene SCN10A and heart conduction disease.