Summary Cardiovascular diseases represent a major cuase of death in the western world. Both nitric oxide and peroxynitrite have been implicated in different cardiovascular processes. Nitric oxide is an endogenous vasodilator and mediator of several important physiological processes and it is involved in a number of protective mechanisms in cells. However, overproduction of nitric oxide can occur and this can lead to cytotoxicity. On the other hand, peroxynitrite is a potent biological oxidant formed from the near-diffusion limited reaction between superoxide anion and nitric oxide. It has been associated with mechanism of cell death such as necrosis and more recently with apoptois. In this review, were discussed some of the various roles of both, and their implicance in physiological and