Minimally invasive cardiac surgery (MICS) has been developed to offer patients the benefits of open heart operations with limited skin incision, but this procedure tends to be more difficult than conventional methods. We tried to evaluate whether MICS would be reasonable as a standard operation for congenital heart defects. From August 1997 to March 2000, 42 patients with atrial septal defects (ASD) and 47 patients with ventricular septal defects (VSD) underwent total repair by the minimal skin incision and lower partial median sternotomy. Fifteen ASD patients and 6 VSD patients were enrolled by residents (resident group). Twenty-seven ASD patients and 41 VSD patients were treated by leading surgeons (staff group). We compared the clinical course of the patients between resident and staff groups. Operative time, bypass time and cardiac arrest time (VSD) of the staff group were clearly shorter than those of the resident group (p<0.05). Other clinical course parameters of the two groups showed no significant difference. The results of this study indicate that MICS for ASD and VSD is reasonable as a standard operation because there was no significant difference of postoperative clinical course except the time required for the operation.