Pulmonary hypertension is present when the mean pulmonary pressure is increased above 25 mm Hg in a rest or above 30 mm Hg during exercise. It is possible to divide it from different point of view. Well known is pathophysiologic classification and Venice classification suggested by WHO symposium 2003. The rise of arterial pulmonary pressure is caused by three essential abnormalities, these are elevated pulmonary vascular resistance, blood flow and pulmonary artery wedge pressure. Vasoconstriction, remodeling of vessels and in situ trombosis are pathogenetic mechanism which contribute to rise of pulmonary hypertension.

        Key words: Pulmonary hypertension - Venice Classification - Vasoconstriction - Remodeling of vessels