Comparison of Porcine Biological Valves with Pericardial Valves - a 12-Year Clinical Experience with 1123 Bio-Prostheses - Reichenspurner, H; Weinhold, Ch; Nollert, G; Kaulbach, H G; Vetter, H O; Boehm, D H; Reichart, B (The Thoracic and Cardiovascular Surgeon, 1995)