INTRODUCTION: In patients with chronic obstructive pulmonary disease (COPD), oxygen delivery to the heart may be impaired during travel at altitude. We assessed electrocardiogram (ECG)-derived signs of cardiac ischemia and the effects of preventive acetazolamide therapy in COPD patients traveling to high altitudes. METHODS: Patients with COPD [Global Initiative for Chronic Obstructive Pulmonary Disease (GOLD) grades 2-3] and a predicted forced expiratory volume in 1 s (FEV RESULTS: At 760 m, 3 of 49 (6%) patients randomized to placebo and 3 of 50 (6%) randomized to acetazolamide showed a post-exercise STE. At 3,100 m under placebo, two (4%) new STEs developed and one (2%) disappeared compared to 760 m ( CONCLUSIONS: In lowlanders with moderate to severe COPD ascending to 3,100 m, no ECG-derived signs of cardiac ischemia emerged neither at rest nor post-exercise and this was not modified by preventive acetazolamide therapy.