Cyclic AMP (cAMP)-dependent chloride channels modulate changes in resting membrane potential and action potential duration in response to autonomic stimulation in heart. A growing body of evidence suggests that there are marked similarities in the properties of the cAMP-dependent chloride channels in heart and cystic fibrosis transmembrane regulator (CFTR) chloride channels found in airway epithelia or in cells expressing the CFTR gene product. We isolated poly A+mRNA from rabbit ventricle and converted it to cDNA for amplification using the polymerase chain reaction (PCR). A fragment corresponding to the nucleotide-binding domain 1 (NBD1) of the CFTR transcript was cloned. Comparison of the amino acid sequence of NBD1 of human CFTR with the deduced sequence of the rabbit heart PCR product indicated 98% identity. Northern blot analysis, using the heart amplification product as a cDNA probe, demonstrated expression of homologous transcripts in human atrium, guinea pig and rabbit ventricle, and dog pancreas.Xenopusoocytes injected with poly A+mRNA extracted from rabbit and guinea pig ventricle or dog pancreas expressed robust time-independent chloride currents in response to an elevation of cAMP. We conclude that CFTR chloride channels are expressed in heart and are responsible for the observed cAMP-dependent chloride conductance.