The investigators are studying what causes Plastic Bronchitis and Protein Losing Enteropathy. The investigators think that these problems are from too much of two small proteins called Vasoactive Intestinal Peptide (VIP) and Substance P. VIP and Substance P are important proteins in the body that normally tell the body to make small amounts of fluid and they help the intestines work. Normally, VIP and Substance P are made in the intestines and then destroyed in the lungs after they do their normal work. The investigators think that kids who have Plastic Bronchitis and/or Protein Losing Enteropathy who also had the Fontan surgery might have too much VIP and Substance P in their bodies. The investigators think this causes too much fluid to go in the lungs and too much protein in the intestines.