It is essential that the factors leading to bioprosthelic valve dysfunction are fully understood if a more durable bioprosthesis is to be developed and the incidence of premature failure reduced. Studies of explanted bioprostheses yield important information on both the aetiology of valve failure and influence of valve/host interactions. Details are given of the Sheffield Explant Study which holds data on 570 explants and 34 different models. Advantages and disadvantages of this type of study are discussed.