Anatomical rules that make it possible to accurately replace mitral anterior cusp chordae tendineae with tanned xenograft pericardium are defined. Anterior and posterior cusp chordae were replaced with xenograft and autologous pericardium in 11 patients who had ruptured or elongated chordae. The xenograft occasionally became calcified; however, because it did not become elongated or shortened, competence was maintained for up to 3 years. Insufficiency was corrected, and the correction maintained for up to 4 months. Degenerative disease proved easier to treat than rheumatic disease. Two-dimensional echocardiography was a valuable aid in both preoperative planning and postoperative evaluation.