The present investigation was designed to study cardiohemodynamics and endothelium-dependent vascular reactivity estimated by the reactive hyperemia – one of the endothelium-dependent vascular responses – in 55 healthy highlanders (2,200 m a.s.l.) compared to 55 healthy lowlanders matched by sex, age, body weight and height. Among the basic parameters of the central hemodynamics and myocardium contractility, there was revealed statistically significant increase in diastolic blood pressure, stroke volume and blood flow rate in the highlanders. The stroke volume increment was stipulated by rising in myocardial contractile activity. A mild hypertrophy of the myocardial ventricles and signs of pulmonary hypertension were observed in the highlanders much more often than in the residents of sea level. The endothelium-dependent reactive hyperemia simulation revealed more pronounced vasodilator responses in the highlanders. The peak values of the forearm blood flow, both absolute and relative, were significantly higher compared to those in the lowlanders. The obtained results allow to make a conclusion that continuous action of moderate hypoxia causes strengthening in cardiac pump and contractile functions, increase in endothelium-dependent vascular reactivity and widening the vasodilator reserve due to increasing the production and/or release of vasodilator agents, in particular nitric oxide. Such widening of the vasodilator reserve might be considered as one of the adaptive mechanisms of cardiovascular regulation in extreme conditions.