A description is presented of the gross anatomic, histologic, and scanning electron microscopic features of cuspal abrasions, perforations, and tears caused by excessively long ends of braided sutures in bioprosthetic cardiac valves implanted in the mitral position in sheep. These lesions are produced as consequences of contact between the ends of the sutures and the inflow surfaces of the bioprosthetic cusps, leading to a process of surface erosion that progresses to actual perforation of the cusps. The perforation has the appearance of a crater, the wider end of which faces the inflow surface and the walls of which are formed by broken ends of collagen fibrils. Suture perforations can extend to form tears that involve the free edge of the cusp and result in hemodynamically important regurgitation. Therefore, care must be taken to avoid leaving excessively long suture ends during the implantation of bioprosthetic cardiac valves.