GPR35 and heart failure: G protein–coupled receptor 35 (GPR35) is a poorly characterized orphan G protein-coupled receptor (GPCR), which has potential therapeutic value based on its association with several diseases, including cancer, inflammatory bowel disease, diabetes, hypertension, and heart failure.1 Despite reports linking it to several endogenous molecules, including kynurenic acid2 and the chemokine CXCL17,3 its endogenous ligand and biological function remain undefined.4