Among the tetrodotoxin-resistant(TTX-R) α-subunits, Nav1.5 mRNA showed the strongest expression in the heart, according with its consideration as the cardiac Na⁺ channel. Compared to its mRNA transcription in the heart, the Nav1.5/SCN5A gene was also expressed in high levels in the brain, especially limbic regions of the brain. Exon6A of Nav1.5/SCN5A gene was first found in cloning of Nav1.5 channel in human neuroblastoma cells. It was found that it is exon6A that encodes Nav1.5 channels in human and rat brain while it is exon6 that encodes Nav1.5 channels in other tissues in the cloning of Nav1.5 channel in these tissues, Both exon6A and exon6 have 92 base pairs, which encodes 30 amino acid residues, and are located in human chromosome 3. But these two resulting products differ by 7 amino acid residues. There is only one different base pair between the enon6As encoding Nav1.5 channels in human and rat brain, but their encoding amino acid residues are identical. The expressions of exon6A in different part of the brain are different and the similar result was found in the expressions of exon6 among different tissues of rat when detected by using RT-PCR method. The study is useful for making further investigation in the functional analysis of Nav1.5 channels in different tissues.