Parasympathetic withdrawal increases heart rate after 2 weeks at 3454 m altitude

Heart rate is increased in chronic hypoxia and we tested whether this is the result of increased sympathetic nervous activity, reduced parasympathetic nervous activity, or a non‐autonomic mechanism. In seven lowlanders, heart rate was measured at sea level and after 2 weeks at high altitude after individual and combined pharmacological inhibition of sympathetic and/or parasympathetic control of the heart. Inhibition of parasympathetic control of the heart alone or in combination with inhibition of sympathetic control abolished the high altitude‐induced increase in heart rate. Inhibition of sympathetic control of the heart alone did not prevent the high altitude‐induced increase in heart rate. These results indicate that a reduced parasympathetic nervous activity is the main mechanism underlying the elevated heart rate in chronic hypoxia.