The biological effects of histamine are mediated through four receptors (H1- H4 Histamine receptors) all of which belong to the 7-transmembrane domain, G protein-coupled receptor (GPCR) superfamily.nH2 receptors couple to adenylate cyclase via Gs, leading to the formation of cAMP and the activation of protein kinase A (PKA).nH2 receptors are expressed in several tissues including brain, gastrointestinal tract and heart.nThe most studied physiological role of the H2 receptors is their involvement in the regulation of gastric acid secretion.Specific H2 receptor antagonists are currently used for the treatment of acid-related gastrointestinal conditions such as peptic ulcer, gastroesophageal reflux disease and dyspepsia.nInvolvement of H2 receptors in chronic heart failure and immune regulation has also been suggested.