Nitric oxide has been implicated in the regulation of cardiac contractile function as well as the depressed myocardial contractility associated with sepsis and endotoxemia. We examined the effects of nitric oxide synthase (NOS) inhibitors and a nitric oxide generator on contractile responses of left atrial preparations and ventricular myocytes isolated from endotoxemic guinea pigs, which exhibit depressed myocardial contractile function. The NOS inhibitor L-NAME had no effect on contractile tension developed by control atria or atria isolated from guinea pigs 4 or 16 h after an intraperitoneal injection of endotoxin. Similarly, contraction of ventricular myocytes isolated from control or endotoxemic guinea pigs (4 h after endotoxin injection) was unchanged by exposure to several NOS inhibitors. In addition, neither Ca2+-dependent nor Ca2+-independent ventricular NOS activity was affected by endotoxemia. These data suggest that nitric oxide alone is not responsible for the cardiac contractile dysfunction of endotoxemic guinea pigs.