Nitric oxide (NO) is a unique, endogenous regulatory molecule that is involved in a wide variety of physiological processes in multiple organ systems. This simple gas functions as a cellular messenger in a broad range of biological activities that include blood pressure regulation, immunomodulation and neurotransmission. It has also been implicated in a number of homeostatic functions in the cardiovascular system: it is a significant determinant of basal vascular tone and, in addition is thought to regulate myocardial contractility and platelet aggregation. Dysregulation of NO mediated effects have been implicated in the pathogenesis of essential hypertension, atherosclerosis, and the hypotension associated with septic shock. This review will focus on these multiple effects of NO in the cardiovascular system.