RNA-seq was conducted on heart tissue from white shark (Carcharodon carcharias), shortfin mako (Isurus oxyrinchus), great hammerhead (Sphyrna mokarran), yellow stingray (Urobatis jamaicensis), swordfish (Xiphias gladius), hogfish (Lachnolaimus maximus), and ocean surgeonfish (Acanthurus bahianus). Heart transcriptomes were assembled in order to determine differences in gene content between elasmobranchs and teleost fishes as well as between regional endothermic species (white shark, mako, and swordfish) and pure ectotherms (great hammerhead, yellow stingray surgeonfish, and hogfish). We identified cases where positive selection was acting on the elasmobranch lineage and genes that had functional differences between elasmobranchs and teleosts with a focus on immune genes.