Mean arterial pressure (MAP; A), mean pulmonary arterial pressure (PAP; B), systemic vascular resistance (SVR; C), pulmonary vascular resistance (PVR; D), cardiac output (E), and plasma methemoglobin concentration (F) of awake lambs after infusion of 37°C autologous whole blood (12 ml/kg) (n=6), after intravenous HBOC-201 (n=5), or HBOC-201 (12 ml/kg) after pretreatment with a sodium nitrite infusion (1 mg/kg over 5 min; n=4). *p<0.05 HBOC-201 differs from autologous blood and from HBOC-201 after nitrite, †p<0.05 autologous whole blood differs from HBOC-201 with or without nitrite infusion, ‡p<0.05 HBOC-201 after nitrite differs from autologous whole blood, §p<0.05 differs from before nitrite administration.