Pulmonary hypertension syndrome (PHS) in broiler chickens adequately represents idiopathic pulmonary arterial hypertension (IPAH) in humans, a condition that affects 300 new patients each year in the US. The factors that trigger IPAH are poorly understood but an increase in reactive oxygen species in the circulation coincides with the onset of these conditions. Broiler chickens (n=583) were fed a control diet (CTL), containing 3,200 kcal of ME / kg of feed, 23% CP, 1.55% (wt / wt) Arginine (Arg) and 40 IU of VE (alpha-tochopherol) / kg of feed; a high-Arg diet (HA), CTL diet plus 0.8% (wt / wt) supplemental L-Arg HCl; or a high Arg and vitamin diet (AEC), the HA diet plus 200 IU ?-tochopherol / kg of feed and 500 mg of ascorbic acid / L of drinking water 500 mg ascorbic acid / L of water (exp. 1 and 2) or Kg feed (exp. 3). Supplemented broilers were either exposed to hypobaric hypoxia or had a primary bronchus occluded (PBO) to induce PHS. Also, medial thickness was assessed in male broiler and Leghorn (n =80) chickens fed a CTL diet and subjected to pulmonary artery occlusion (PAO). The results show that supplementation with Arg and VE plus VC have an additive effect on the velocity at which the pulmonary arterial pressure returned to basal levels in hypoxic chickens challenged with epinephrine. Also, supplementation increased xanthine oxidase (XO) activity in the vicinity of the pulmonary endothelium with no effect on NAD(P)H-oxidase activity or oxidative stress in hypoxic chickens subjected to PBO. These enzymes are upregulated in humans with IPAH. Furthermore, supplementation reduced pulmonary artery reactivity to phenylephrine in hypoxemic broilers. Unsupplemented broiler chickens had a lower specific lung weight compared to unsupplemented Leghorns. Hypoxemic broilers showed thicker resistant pulmonary arteries and were more hypertensive than hypoxemic Leghorns. Leghorns were more hypoxemic and resistant to PHS than broilers. In conclusion, Arg and VE plus VC show an additive effect in the improvement of cardiovascular performance of hypoxemic broilers as well as in restoring reactivity to phenylephrine in hypoxemic pulmonary rings. Also, supplementation shows an additive effect in restoring XO activity in hypoxic broilers. Leghorns had a better ventilation capacity and better pulmonary vasodilation capacity than broiler chickens.