39 children patients with acyanoid ventricular septal defect or atrial septal defect who received cardiac operation, were compared with a age and sex matched normal control group on a battery of neuro-psychological tests, intelligence tests and children behavioral checklist. Subject were examined prior to cardiac operation and 6 months after the operation. 12 of 39 children received postoperation tests. Among them, 8 were in younger children group (5 to 8 years old), 4 were in elder children group (9 to 14 years old). Results are: 1. Neuropsychological development status: (1) Full IQ(FIQ), Verbal IQ(VIQ), and Performance IQ(PIQ) of the group with heart diseases were lower than those of normal controls, and there were significant differences. (2) In cardiac patients significant impairments were found on some scores of the Halstead-Reitan Battery in comparison with the normal control group. These findings imply that patients before cardiac operation had generalized impairments in neuropsychological function. (3) Significantly more behavioral problems especially the so called externalizing and internalizing behavioral problems, were found in cardiac patients than the controls. 2. Comparison of the pre and post operative scores were made: Both groups (cardiac patients and controls) showed significant improvements in VIQ, PIQ, FIQ and most of H-R subtests scores 6 months later. But the improvements following surgery were attributed to practice effects.