People with heart disease are very susceptible to the effects of altitude, especially when on airplanes, mountain climbing, hot air balloon rides. High altitude increases cardiac output, increases heart rate, increases breathing rate and contractility of the heart, adversely affecting cardiovascular health if not prepared for countermeasures.

The effects of altitude make breathing more difficult, potentially leading to altitude sickness due to lack of oxygen, which is life-threatening if the body has not been trained to adapt to high altitude climate conditions.