A total of 800 broiler chickens was studied; 400 at sea level, and 400 at an altitude of 3,300 m. Only the chickens raised in this latter condition showed an increased mean pulmonary arterial pressure (mPap), weight of the right ventricle relative to that of both ventricles (RV/TV), hemoglobin concentrations, hematocrit value and red blood cell count. A high correlation between mPAP and RV/TV was found. 20% of the chickens raised at high altitude died with signs of right heart failure. The calculated mPap in these birds was found to be greater than that of the high altitude birds which did not develop overt signs of cardiac insufficiency. These results indicate that some broiler chickens raised at high altitude develop right heart insufficiency secondary to pulmonary arterial hypertension.