Gross observation at the slaughterhouse determines the primary selection of porcine aortic valves for the manufacture of bioprostheses. This step is critical because only valves with significant abnormalities are rejected. The present study validated this selection process by investigating the pathological characteristics of one series of accepted valves and one series of rejected valves. Macroscopy, x-ray examination, light microscopy, and scanning electron microscopy (SEM) were performed on 5 initially rejected valves, 3 leaflets from 3 other initially rejected valves, and 6 valves that successfully passed this first step in the selection process. Abnormalities were macroscopically visible only on the rejected valves and were described as thick white areas, heavy white striations, thin spots, white plaques, and nodules. Individual variability in the structure of each leaflet was more significant in the rejected valves than in the valves that had passed the first inspection. The leaflets of the rejected valves were also irregularly thick with a lack of consistency in the position and prominence of the different layers. The formation of nodules and the presence of white plaques in the inner fibrosa layer were among the pathological features. The initially accepted valves considered defect free under gross observation continued to display some weaknesses, and not all of the valves selected during the first step of the process were suitable to become bioprostheses. Because the manufacturer carries out further quality control inspections at every step of preparation resulting in additional rejections, it is therefore anticipated that all valves with defects will be rejected. None of the rejected valves were defect free, and rejection was fully justified.