Per rectal portal scintigraphy using 99"Technetium pertechnetate (99"T~04-) was used to diagnose portosystemic shunts (PSS) before surgical confirmation in seven dogs and two cats. Shunt fractions, representing the percent of portal blood that bypasses the liver, were determined by computer analysis of the scintigraphic images. Animals with portosystemic shunts had a mean preoperative shunt fraction of 84.02% (n = 9). The mean postoperative shunt fraction in four animals was 58.22%. The mean shunt fraction in ten control dogs was 5.00%. Per rectal portal scintigraphy is an innovative, easily performed, inexpensive method to diagnose congenital portosystemic shunts in dogs and cats. (Journal of Veterinary Internal Medicine 1991; 523-27)

Per‐rectal portal scintigraphy using tech‐netium‐99m pertechnetate (99mTcO4‐) was performed in 8 normal dogs before and after surgical creation of a portacaval shunt. Shunt fractions were calculated by computer assisted analysis of dynamic images (IMG) and compared to shunt fractions determined by mesenteric venous injection of radioactive microspheres (MIC). The mean pre‐operative shunt fraction was 1.59% using IMG and 3.00% using MCI. The mean postoperative shunt fraction was 64.56% using IMG and 69.56% using MIC. There was excellent correlation between both methods (r2 0.94). Per‐rectal portal scintigraphy is an easily performed, inexpensive method to diagnose and quantify portosystemic shunts in dogs.