It is estimated that> 140 million people live above 2500 m in various regions of the world. 1 There are many challenges to living at high altitude, but chronic exposure to alveolar hypoxia is prominent among them. Inspired PO2 falls from≈ 150 mm Hg at sea level to≈ 100 mm Hg at 3000 m and 43 mm Hg on the summit of Everest (8400 m). 2, 3 The body responds by hyperventilating, increasing resting heart rate, and stimulating red cell production in an attempt to maintain the oxygen content of arterial blood at or above sea level values. 2 However, hypoxic pulmonary vasoconstriction (HPV) and vascular remodeling, together with increased erythropoiesis, place an increased pressure load on the right ventricle (RV). How well healthy humans adapt to hypoxia depends on their rate of ascent to altitude, the severity and duration of their exposure, and their genetic background.