Figure 4: Representative photomicrograph of small pulmonary artery from two-year-old male bull born and raised at altitude of 3000 m. Views of lung tissue at low (a) and high (b) magnification show prominent medial thickness and enlarged outer layer of pulmonary artery with accompanying small airway (H&E stain). Ratio of RV/LV and mPAP of this bull were 0.545 and 70 mmHg, respectively. Arrows: small pulmonary artery.