Since the isotopes can not be utilized for veterinary patients in Japan, the authors developed a simple calculation formula of shunt fraction of portosystemic shunt based on the hepatic circulation model. The shunt fraction can be calculated utilizing only 2 portal pressure measurements of pre-shunt ligation and temporary or permanent shunt ligation. The calculated shunt fraction can obtained pre-ligation and post-ligation either temporally or permanent complete shunt ligation: complete ligation group of PSS (n=59) had 48.2 +/- 16.9% of shunt fractions, whereas the partial ligation group (n=48) had 71.6 +/- 10.7% of shunt fractions.