The Angiotensin II Receptor, Type 1 (AGTR-1), also known as AT1, is a member of a family of seven transmembrane G protein-coupled receptors that mediates the effects of Angiotensin II, the major bioactive peptide of the renin-angiotensin system. AGTR-1 is 359 amino acids (aa) in length with a predicted molecular weight of 41.1 kDa. Human AGTR-1 shares 94% and 95% aa sequence identity with mouse and rat orthologs, respectively. Interestingly, most species express a single AGTR-1 gene while rodents contain two related genes, which are termed AGTR-1A and AGTR-1B. AGTR-1 is widely expressed with the highest levels being found in the liver, kidney, adrenal glands, brain, heart, vasculature, and lungs. It is coupled to G proteins containing the alphaq/11 subunits and has been shown to activate the PLC-IP3-Ca2+ and PLC-DAG-PKC, MAPK, and Jak/STAT signal transduction pathways. AGTR-1 has been shown to mediate most of the physiological actions of Angiotensin II including vasoconstriction, aldosterone and vasopressin release, salt and water retention, cell proliferation and migration, and sympathetic stimulation. Additionally, AGTR-1 has been suggested to play a role in the induction of reperfusion arrhythmias. AGTR-1 antagonists are used to treat hypertension, diabetic nephropathy, and congestive heart failure.