Background: In patients with Tetralogy of Fallot (TOF) who were corrected by operation, there are uncertain aspects for left ventricle dysfunction though right ventricle dysfunction has been known already. By several established studies, left ventricle dysfunction (LV dysfunction) was related to paradoxical interventricular septal motion, ventricular dyssynchrony, and decreased myocardial deformation. We aim to analysis of major factors of left ventricle dysfunction in patients with TOF who were corrected by using electrocardiography (ECG), echocardiography, and cardiac MRI. Methods: We reviewed ECG, echocardiography, and cardiac MRI in patients with TOF who were corrected. We subjects to 76 of 139 patients with TOF and fallot type DORV who could be available data of ECG, echocardiography, and cardiac MRI, except for patients with pulmonary atresia and significant aortic regurgitation. The LV dysfunction group was defined as patients with ejection fraction of left ventricle ��� 55% in cardiac MRI. The quantification of paradoxical septal motion was assessed from parasternal short-axis images at the papillary muscle level in echocardiography. The paradox index was calculated by dividing the ratio short to long diameter at end-systole by the ratio at end-diastole. We measured global longitudinal strain in 4 chamber view on echocardiography for analyzing of myocardial deformation. And then, we compared to QRS duration on ECG, the paradox index, and global longitudinal strain in 4 chamber view on echocardiography between normal left ventricular function and dysfunction group. The data were analyzed using the SPSS statics 17.0. Results: Totally 76 patients consisted of 44 males and 32 females. Their mean age at the time of cardiac MRI was 18.9짹6.41 years old and 23 patients were identified by LV dysfunction group by cardiac MRI. In comparison between both groups, there are no differences in ages, time at cardiac MRI from totally correction, ages at palliative shunt, time at totally correction from palliative shunt, and ages at totally correction between both groups. In analysis of factors related to LV dysfunction, there is significant difference in QRS duration on ECG and paradox index (140.0짹22.5 vs 163.3짹24.4ms; 1.20짹0.12 vs 1.13짹0.11; normal LV function vs LV dysfunction group) though no difference in global longitudinal strain on echocardiography. In statistical analysis, the paradox index is more significant for LV dysfunction. Conclusions: In our study, significant factor of LV dysfunction is paradoxical interventricular septal motion and ventricular dyssynchrony, and the paradoxical ventricular septal motion is more significant factor.