Waldenstromʼs Macroglobulinaemia (WM) is a rare haematological lymphoma that causes numerous haemostatic complications due to the elevated levels of immunoglobulin M (IgM) circulating in the blood. These complications, such as hyperviscosity syndrome, may be exacerbated by the physiological effects of cardiopulmonary bypass (CPB). In this case study, a 45-year-old male suffering from WM underwent an emergency aortic valve replacement, closure of an atrio-ventricular fistula and mitral valve repair. He was found to have an elevated blood viscosity, anaemia and hypervolaemia prior to surgery. These complications remained a problem during CPB, leading to a large circulating volume, but a low haemoglobin, requiring haemofiltration and blood transfusions whilst limiting any further rise in blood viscosity. The situation was further compounded by the presence of electrolyte disturbances. It was concluded that a careful balance between blood conservation techniques and temperature management was required to reduce hyperviscosity and anaemia, but maintain organ protection. In future, given more time, modern plasmapheresis techniques could be used for acute management of WM during CPB.