Portopulmonary hypertension (PPH) is the coexistence of pulmonary arterial hypertension (PAH) and portal hypertension in patients with or without cirrhosis. PAH may develop in 2-6% of patients with portal hypertension and is the result of complex pathophysiological interactions between the portal and pulmonary circulations. The pathogenic mechanisms are unknown and depend both on the underlying severity of the liver disease and on the adaptation of the heart to the disease of the pulmonary vessels. Various pathophysiological aspects appear to be involved in the development of PPH, including angiogenesis, genetics, humoral changes, and inflammation with increased pulmonary phagocytosis. Female gender and estrogen metabolism with elevated estrogen levels are associated with the development of PPH. Of particular interest is the activation of powerful local vasoconstrictor systems, the imbalance between vasoconstrictors and vasodilators, which contributes to the narrowing of pulmonary vessels. Increased pulmonary blood flow causing shear stress can lead to endothelial damage and dysfunction with vasoconstriction and progressive vascular remodeling. However, only a small number of patients develop PPH, which indicates the involvement of other factors. Therefore, other numerous theories have been proposed that require further study.