Porcine small intestine submucosa fashioned into a pulmonary valve leaflet was used to replace single excised leaflets in four swine. Animals were sacrificed at various postoperative times up to 111 days after implantation. Through time, the small intestinal submucosa leaflets were resorbed and replaced with histologically similar host tissue. Apposition between substitute leaflet and host leaflets was maintained. Valvular competency, as determined by echocardiography, was normal throughout remodeling, and the replaced valve grew proportionately with each animal. Porcine small intestine submucosa may have clinical significance as a biocompatible material used for cardiac valve repair and replacement.