A 74-year-old man with cardiac failure and renal impairment was admitted to the cardiothoracic intensive care unit with metformin-induced lactic acidosis and shock. He was successfully treated with high-dose (80 ml/kg/hour) continuous venovenous haemodiafiltration. Lactic acidosis is a known complication of metformin and is associated with a high mortality. The use of high-dose continuous venovenous haemodiafiltration for this condition has not previously been reported.