An association between aortic stenosis and haemorrhage from gastrointestinal angiodysplasia has been recognised for many years, but no explanation for this link has been found. Remarkably, aortic valve replacement, rather than bowel resection, corrects the bleeding. Aortic stenosis can be complicated by acquired von Willebrand's disease type IIA (vWD-IIA), which is corrected after valve replacement, and gastrointestinal angiodysplasia is a common site of bleeding in older patients with acquired or congenital vWD. Could the stenotic aortic valve lead to an acquired, reversible deficiency of the largest multimers of plasma von Willebrand factor (equivalent to vWD-IIA) and thus explain the association with gastrointestinal haemorrhage?