Tilarginine is L-N-monomethyl arginine (L -NMMA), a non-selective inhibitor of nitric oxide synthase (NOS), which has been studied in the treatment of septic shock and cardiogenic shock complicating myocardial infarction. Despite strong evidence that excessive nitric oxide (NO) production plays a pivotal role in the pathogenesis of septic shock and may contribute to the pathogenesis of cardiogenic shock complicating myocardial infarction, outcome studies in these two disorders have proved disappointing. Tilarginine therapy was associated with an excess mortality, particularly at doses > 5 mg/(kg h), in septic shock, whereas the effects of a lower dose (1 mg/(kg h)) in cardiogenic shock complicating myocardial infarction were neutral. The excess mortality in patients with septic shock was almost certainly the result of unfavorable hemodynamic changes induced by Tilarginine (decreased cardiac output, increased pulmonary vascular resistance and reduced tissue oxygen delivery) whereas the lack of benefit in patients with cardiogenic shock complicating myocardial infarction may have been because the dose of Tilarginine was too low.