Two tachykinin-related peptides (TRPs) are known in decapods, APSGFLGMRamide and TPSGFLGMRamide. The former peptide appears to be ubiquitously conserved in members of this taxon, while the latter has been suggested to be a genus (Cancer)- or infraorder (Brachyura)-specific isoform. Here, we characterized a cDNA from the American lobster Homarus americanus (infraorder Astacidea) that encodes both TRPs: six copies of APSGFLGMRamide and one of TPSGFLGMRamide. Mass spectral analyses of the H. americanus supraoesophageal ganglion (brain) and commissural ganglia confirmed the presence of both peptides in these neural tissues; both isoforms were also detected in the midgut. Physiological experiments showed that both APSGFLGMRamide and TPSGFLGMRamide are cardioactive in H. americanus, eliciting identical increases in both heart contraction frequency and amplitude. Collectively, our data represent the first genetic confirmation of TRPs in H. americanus and of TPSGFLGMRamide in any species, demonstrate that TPSGFLGMRamide is not restricted to brachyurans, and show that both this peptide and APSGFLGMRamide are brain-gut isoforms, the first peptides thus far confirmed to possess this dual tissue distribution in H. americanus. Our data also suggest a possible role for TRPs in modulating the output of the lobster heart.