A cor triatriatum sinistrum was successfully treated by operation in a 14-week-old infant of a Jehovah's Witness family. The child was pretreated with erythropoietin until a hemoglobin level of 14 g/dl was obtained. There was no cardiac catheterization before the operation. The operation was performed with cardiopulmonary bypass. No blood products were transfused and the hemoglobin level after performing modified ultrafiltration was 11.5 g/dl. The infant was extubated on the same day and discharged from our institution on the eighth day after surgery. Two years after surgery the child is in sinus rhythm and is developing well.