The present invention relates to an isolated or purified human nucleic acid, preferably a DNA, comprising a nucleotide sequence encoding an I.sub.h ion channel. The invention further relates to a vector comprising the isolated or purified nucleic acid, a host cell comprising the vector, and a composition comprising the isolated or purified nucleic acid and a carrier therefore. The invention also provides a polypeptide or protein encoded by the nucleic acid, and a method of treating a mammal for a cardiovascular disorder.