Objective    To improve beating heart intracardiac operation technique with mild hypothermic cardiopulmonary bypass

and to review the clinic experience in 134 infants with atrial septal defect between January 1999 and July 2007.     Methods    Totally 134 infants below 3 years of age

with a mean age of (15.1±6.8) months

weighing 5-16 kg

were included

among whom 112 infants showed delayed growth or dyspnea

79 were administered emictory for heart failure and increasing cardiomegaly

101 had the isolated defect

and 33 had minor associated lesions requiring additional procedures. Beating heart surgery with cardiopulmonary bypass were performed in all infants.     Results    All infants survived. One infant was found to have sinus node dysfunction and managed. A total of 110 infants followed up from 2 months to 4 years showed improvement in growth and development.     Conclusion    Operation should be performed on infants with ASD when the operation indication is confirmative. Beating heart surgery with cardiopulmonary bypass is a safe and reliable procedure for the infants with ASD.