Portal hypertension is defined as elevated pressure in the portal venous system, most commonly caused by cirrhosis. On Doppler ultrasound, portal hypertension manifests as reduced portal vein velocity (normal >16 cm/s), bidirectional (to-and-fro) flow, or complete reversal of portal flow (hepatofugal flow). Associated findings include splenomegaly, ascites, and portosystemic collateral vessels (varices). Doppler evaluation of the portal system is a routine component of liver ultrasound in patients with known or suspected liver disease.