20 ml samples of heparinised blood and urine will be taken from the arterial line or urine catheter. Samples will be taken immediately after the preoperative insertion of the arterial/urine catheter, at 6, 24, 48, 72, 96 and 120 hours after commencement of cardiopulmonary bypass. Immediately following collection, the preoperative, 6 and 24 hour blood and urine will be centrifuged at low speed to separate the plasma from the cellular components. Urine and plasma and full-blood (for COMT polymorphism) will be stored in aliquots (where necessary) at -70 degrees prior to batch analysis.