It has been shown, that subjects susceptible to high altitude pulmonary edema (HAPE)are characterized by an abnormal increase of pulmonary artery pressure at rest in hypoxia and during exercise in normoxia. This abnormal rise of pulmonary artery pressure has also been observed in about 10 % of otherwise healthy subjects without prior altitude exposure. The aim of the study is to investigate the susceptibility to HAPE in unacclimatized subjects with abnormal increase of pulmonary artery pressure at rest in hypoxia and during exercise in normoxia after rapid ascent to high altitude (4559 m).