Figure 3: Representative photomicrograph of small pulmonary artery from pure-bred, domesticated two-year-old male yak living at high altitude. Views of lung tissue at low (a) and high (b) magnification show absent thickening in pulmonary artery with accompanying small airways (H&E stain). The RV/LV and mPAP of this yak were 0.315 and 25 mmHg, respectively. Arrow: small pulmonary artery.