Reduced Hb-O₂ affinity facilitates O₂ release to tissue but may impair pulmonary O₂ uptake, affecting cardiac output and systemic vascular resistance (SVR). We studied the effects of shifting the O₂-dissociation curve (ODC) to the right with a continuous infusion of RSR13, an allosteric modifier of Hb, and of different inspired O₂ fractions (FI_O2) on arterial O₂ saturations (Sa_O2) in Hb and on hemodynamics in nonanesthetized rats. At an FI_O2 of 0.21, Sa_O2 fell during RSR13 from 95 to 81%. Elevation of FI_O2 to 0.30 returned Sa_O2 to baseline in the RSR13 group. The decrease in mean arterial pressure (MAP) was significantly greater in the control than in the RSR13 group at 30% O₂. Cardiac index (CI) increased only during RSR13 at 21% O₂ and returned to baseline at 30% O₂. In contrast, SVR decreased after RSR13 was infused at 21% O₂ but returned to baseline at 30%O₂, whereas controls showed the opposite, a sustained SVR. In the follow-up period, when 21 O₂% was reestablished and mild anemia was present, MAP and SVR fell significantly more in controls, whereas CI only increased in controls. Lactate was significantly lower in the RSR13 than in the control group during RSR13 and the follow-up period. These results demonstrate that 1) continuous infusion of RSR13 produces a constant shift in the O₂ tension at which Hb is 50% saturated (P₅₀), 2) FI_O2 of 0.30 compensates for the effects of increased P₅₀ on pulmonary O₂ loading, and 3) right-shifted ODC combined with supplemental O₂ may improve tissue O₂ availability.