Objective This study is aimed to evaluate the value of real-time three-dimensional echocardiography (RT-3DE) in the assessment of pre- and post-operative left ventricular function in children with conotruncal defects (CTD). Methods Forty-six consecutive children (mean aged 2.0±2.7 years) with CTD were examined by Phillips RT-3DE System. Their pre- and post-operative left ventriclular function parameters (one month after surgical operation) such as volume, stroke volume and ejection fraction were estimated by Tomtec RT-3DE apical longitudinal 8-plane method. The results were compared and assessed. using paired t-test and Pearson’s correlation coefficient analysis. Results Compared with pre-operative end-diastolic and end-systolic volume (18.7±14.9 ml and 9.0±7.3 ml) of left ventricle, their post-operative end-diastolic volume (22.2±17.6 ml) was increased, while their post-operative end-systolic volume (9.5±7.8 ml) was not obviously changed in one month after surgical operation. Furthermore, there were good correlations between pre- and postoperative end-systolic volume (r=0.97), and between the pre- and postoperative end-diastolic volume (r=0.95). Accordingly, compared with pre-operative stroke volume (9.6±7.6 ml) and ejection fraction (0.52±0.03), their post-operative stroke volume (12.7±9.8 ml) and ejection fraction (0.58±0.03) were markedly increased (P<0.05). Moreover, compared with pre-operative end-diastolic wall mass (19.4±11.4 g), post-operative end-diastolic wall mass (21.1±11.0 g) was increased. Thus, after cardiovascular deformities of CTD were surgically corrected, cardiac function was early improved and gradually normalized completely. Conclusions By making precise quantitative assessments without geometric assumptions, RT-3DE could be helpful in providing more information for preoperative diagnosis, post-operative follow-up and prognostic prediction in CTD.