Portosystemic shunts are abnormal blood vessels that divert blood away from the liver so that the liver isn't able to process it as it should. When blood bypasses the liver by way of a shunt, the nutrients and waste products carried by that blood cannot be cleaned or processed. Toxins can build up in the bloodstream, and the puppy won’t receive the nutrition it needs to grow and have energy. Such puppies may be unusually small, with poor muscular development and possibly behavioral abnormalities, such as seizures, circling, unresponsiveness, head pressing or just staring into space. These signs are most common within a few hours after a meal, especially a high-protein meal. Your veterinarian can perform tests to diagnose the condition and can outline a special diet and formula that can help. Sometimes surgery is recommended.