It is unknown if nitric oxide (NO) modulates the relative levels of left (LV) and right (RV) ventricular output, fetal O₂ consumption, or blood flow distribution between the body and placenta at midgestation. To address these questions, six fetal lambs were instrumented at 89-96 days gestation (term 147 days), and blood flows were measured with radioactive microspheres 3-4 days later at baseline and after inhibition of NO synthesis with 10 mg/kg (L-NNA₁₀) and 25 mg/kg (L-NNA₂₅) N-nitro-L-arginine. LV output fell by 74 ± 15 ml · min¹ · kg¹ at L-NNA₁₀ (P < 0.005), whereas RV output decreased by 90 ± 18 ml · min¹ · kg¹ at L-NNA₁₀ (P < 0.02) and by a further 80 ± 22 ml · min¹ · kg¹ at L-NNA₂₅ (P < 0.05). As a result, RV output exceeded LV output at baseline (P = 0.03) and L-NNA₁₀ (P < 0.02) but not at L-NNA₂₅. Fetal body blood flow fell by 95 ± 25 ml · min¹ · kg¹ at L-NNA₁₀ (P < 0.01), but because placental blood flow decreased by 70 ± 22 ml · min¹ · kg¹ at L-NNA₁₀ (P < 0.01) and a further 71 ± 21 ml · min¹ · kg¹ at L-NNA₂₅ (P < 0.01), the fetal body-to-placental blood flow ratio was near unity at baseline and L-NNA₁₀ but rose to 1.5 ± 0.3 at L-NNA₂₅ (P < 0.05). In association with these flow changes, fetal O₂ consumption declined by 1.4 ± 0.3 ml · min¹ · kg¹ at L-NNA₁₀ (P < 0.05) and by a further 1.5 ± 0.6 ml · min¹ · kg¹ at L-NNA₂₅ (P < 0.02). These findings suggest that, in midgestation fetal lambs, NO supports an RV flow dominance, whole body O₂ utilization, and the maintenance of a near-equal fetoplacental blood flow distribution.