This randomized placebo-controlled, double-blind, parallel-design trial will evaluate effect of acetazolamide on right heart function in lowlanders with chronic obstructive pulmonary disease (COPD) travelling to high altitude and developping early symptoms and/or signs of impending altitude-illness. Qualifying participants will be randomized 1:1 to acetazolamide or placebo treatment during their further stay of 2 days at 3'100 m.
