The renin-angiotensin system (RAS), also known as the renin-angiotensin-aldosterone system (RAAS) is well known for its role in regulating blood pressure, fluid volume, and perfusion capillary. It is one of the most important systems studied by those interested in the cardiovascular system and by those involved in the pathogenesis of heart and kidney disease. The renin-angiotensin system exists in two structures: a circulating system and multiple local tissue-specific systems. Local RAS have been found in the pancreas, heart, brain, vessels, adrenal glands, and reproductive tract (1). In the classical RAS pathway, the crucial hormone angiotensin (Ang) II is formed by cleavage of angiotensin I. The effects of angiotensin I are mainly exerted by two receptors: the angiotensin II type 1 receptor (AT1R) and the angiotensin type two receptor (AT2R). The physiological attributes and regulations of Ang II vary between tissues. For example, the brain RAS regulates thirst, salt appetite, sympathetic activation, and vasopressin release while the renal RAS regulates fibrosis and sodium retention. In this article, an overview of the components of the renin-angiotensin circulatory system and their production will be provided, along with evidence supporting a cardiac RAS. The local RAS of the heart deviates from the classical pathway in two ways, one being other sources of productions such as myocytes and fibroblasts that differ from renal or neural RAS, and the other being its functions and roles that distinguish it from other tissue RAS. Based on research conducted, the renin-angiotensin system is a critical component that contributes to the progression of heart failure (2). This stimulated further research into RAS suppression in order to control the rate of...... half of article...... (December 6, 1999) The renin-angiotensin-aldosterone system: a specific target for l hypertension management. I am. J. hypertenic. 10.1016/S08957061(99)00103-X7. Danser, A.H.J., Saris, J.J., Schuijt, M.P., & van Kats, J.P. (June 10, 1999) Is there a local renin-angiotensin system in the heart? Cardiovascular Res. 10.1016/S0008-6363(99)00202-38. Kumar, R., Singh, V.P., and Baker, K.M. (April 2009) The intracellular renin-angiotensin system in the heart. Curr. Hypertensive. Rep. 10.1007/s11906-009-0020-y9. Shearer, F., Lang, C.C., & Struthers, A.D. (September 11, 2013) Renin-angiotensin-aldosterone system inhibitors in heart failure. Clinic. Drug. There. 10.1038/clpt.2013.13510. Abadir, PM, Walston, JD, & Carey, RM (September 29, 2012) Subcellular characteristics of functional intracellular renin-angiotensin systems. Peptides. 10.1016/j.peptides.2012.09.016