Editor,—I welcome Thorne’s editorial1 reiterating the pitfalls of overzealous venesection in adults with cyanotic congenital heart disease. As she states there is now a body of opinion highlighting the detrimental effects of inappropriate venesection. The evidence these conclusions are based on, however, is sparse and retrospective. This will unfortunately be a feature of a relatively new field such as adult congenital disease practice until multicentred collaboration and prospective studies are …