Abstract: The present invention relates generally to sodium channel proteins and more particularly to mammalian cardiac sodium channel proteins, to DNA sequences encoding sodium channel proteins, to the polypeptide products of recombinant expression of these DNA sequences, to peptides whose sequences are based on amino acid sequences deduced from these DNA sequences, to antibodies specific for such proteins and peptides, and to procedures for detection and quantitation of such proteins and nucleic acids related thereto, as well as to procedures relating to the development of anti-arrhythmic and cardiotonic drugs.