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High altitude exposure for the purpose of tourism is very popular in mountainous regions and is considered to be safe for patients with stable CAD and preserved LV function. The purpose of this study was to evaluate the haemodynamic response to exercise and electrical stability by Holter monitoring in patients with chronic heart failure (HF) and an EF <40%.We studied 29 HF patients with a peak VO2 >50% of the predicted (25 men, age 60.0 ± 8.9 years, EF 28.8 ± 5.4%) at 540 and 3454 m after an ascent using public transport. Assessments of exercise capacity (cardiopulmonary exercise test), haemodynamic response (inert gas rebreathing system), and susceptibility to arrhythmias (Holter ECG recording) were performed. None of the patients (19 with ischaemic heart disease, 11 with an implantable cardioverter defibrillator) had to return prematurely to the lowland site. Two patients presented symptoms of mild mountain sickness, and one patient developed a self-limited ventricular tachycardia during maximal exercise at high altitude. Mean peak VO2 at the lowland site was 18.5 ± 3.6 mL/min/kg and decreased by 22.2% (P < 0.001) at high altitude. Mean resting heart rate increased from 74.3 ± 12.3 to 83.3 ± 13.4 b.p.m., P < 0.001. No statistically significant difference in premature ventricular contractions (92 ± 150/h at 540 m vs. 111 ± 196/h at 3454 m, P = 0.284) was noted.Patients with stable chronic HF and a peak VO2 >50% of the predicted tolerate a short exposure to an altitude of 3454 m well, even during exercise. However, it cannot be excluded that the susceptibility to ventricular tachyarrhythmias during exercise is increased in some subjects.