Portal Hypertension is a frequent complication of cirrhosis and causes significant morbidity and mortality. Increased intrahepatic resistance is the primary factor but portal hypertension is also associated with changes in systemic and porto-sytemic collateral circulation. Cirrhosis is a state of vasoregulatory imbalance with excess vasoconstrictors and less vasodilators in hepatic circulation and the reverse is true for systemic circulation. Multiple pathophysiologic mechanisms including endothelial dysfunction, sinusoidal remodeling and angiogenesis are involved in increasing resistance in hepatic vascular bed. Current evidence suggests that these changes in vasoreactivity contribute to a significant proportion of intrahepatic vascular resistance and that they are reversible, providing an attractive target for therapeutic intervention.