BACKGROUND: Ultrafiltration, used in pediatric cardiac operations to remove excessive body water, can be separated into conventional and modified techniques according to the connection with the bypass circuit and the time of starting ultrafiltration. Ultrafiltration provides more precise hemodynamic and fluid management immediately after CPB (cardiopulmonary bypass), especially in the pediatric patient. The mechanism by which blood pressure improves remains uncertain. The purpose of this study was to compare the efficacy of ultrafiltration for hemodynamics and reduce the blood consumption amounts in paediatric open heart operations. METHODS: Fourty children undergoing surgical correction of VSD (ventricular septal defect) or ASD (atrial septal defect) were randomly assigned to a ultrafiltration or control group. Conventional ultrafiltration was performed with a polysurphone hemofilter during rewarming of CPB. Modified ultrafiltration carried out in the first 10 to 15 minutes immediately after bypass. In all patients, moderate hypothermic CPB, in the range of 20~25 degrees C body temperature, was performed with nonpulsating flow. RESULTS: Demographic data as well as data from CPB did not differ among the groups. In the ultrafiltration group, significant reductions of the amount of blood transfusion significant increases in systolic pressure and hematocrit were noted in the ultrafiltration group. We have been impressed with what appears to be a marked improvement in hemodynamic status in the modified ultrafiltration process during the first few minutes. CONCLUSIONS: Ultrafiltration has been employed successfully in our hospital, and this study demonstrates that ultrafiltration may help to control water balance, concentration of blood, increase systemic arterial pressure and reduces intraoperative blood transfusion.