5-HT₄ receptors are present in human and porcine atrial myocytes while they are absent from the heart of small laboratory animals. The pig is therefore the only available non-primate animal model to study cardiac 5-HT₄ receptor function under physiological conditions. While several human splice variants of the 5-HT₄ receptor have been described, the splicing behaviour of this receptor in porcine tissue is currently unknown. Here we report on the identification of nine novel C-terminal splice variants of the porcine 5-HT₄ receptor, which were named 5-HT_{4(b2, j, k, l, m, o, p, q, r)}. The internal h-variant was found in combination with several C-terminal exons. In addition, splice variants were found that comprised duplicated exons fused to the common region of the 5-HT₄ receptor, thereby providing evidence for a duplication of the porcine HTR4 gene. One of these variants putatively encoded a nine transmembrane-spanning domain homofusion receptor, 5-HT_4(9TM); also the other variants with a duplicated region might translate into functional, transcriptionally fused dimeric 5-HT₄ receptor variants. The elucidation of the genomic context confirmed that the variants were not genomic artefacts but originated from alternative splicing. This was further corroborated by a functional analysis of the variants 5-HT_4(a), 5-HT_4(r) and 5-HT_4(9TM). To our knowledge, our data are the first to report on a functional GPCR with more than 7 predicted transmembrane domains. These findings urge for caution when interpreting data on 5-HT₄ receptor-related pharmacology obtained in the pig; validation at the molecular level might be needed before extrapolating results to human.