The Na+/H+ exchanger is an integral membrane protein that is universally distribute in mammalian tissues and is responsible for intracellular pH regulation. Several isoforms of the Na+/H+ exchanger exist (NHE-1-NHE-4). The first that was cloned is the amiloride sensitive isoform (NHE-1). Using a fragment of the rabbit cardiac Na+/H+ exchanger cDNA clone we isolated and sequenced Na+/H+ exchanger cDNA from a human heart coding for the complete human Na+/H+ exchanger (NHE-1 isoform). Two overlapping cDNA clones were obtained, giving a combined sequence that contained both 3' and 5' untranslated regions. The 5' and 3' untranslated regions proved to be highly homologous to human sequences described earlier but contained some variations that could affect the mRNA stability and/or the efficiency of translation of the Na+/H+ exchanger. Northern blot analysis and reverse transcriptase polymerase chain reaction confirmed the presence of the 5 kb NHE-1 message in primary cultures of isolated myocytes.