 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 arterialurine 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 will be stored in aliquots at -70 degrees prior to batch analysis. 