Patients with borderline health should consult a physican before travelling to altitude. The physician will need to know the duration of the trip, ascent profile and how much exercise the patient plans to undertake. The presence of comorbid diseases which reduce oxygenation and ventilation should also be taken into account. Every patient must be assessed on an individual basis, there are no clinical investigations which reliably predict outcome at altitude. Patients should not travel to high altitude immediately after an acute coronary syndrome. Most patients with stable coronary artery disease with a sufficiently high exercise capacity at sea level can go as high as 3,000–3,500 m with only a minimally increased risk.