Background: Prolonged observation of children with congenital heart disease (CHD) after surgical correction indicates the development of the myocardial dysfunction. The aim of our study was to characterize markers of myocardial dysfunction in children with CHD after surgical correction. Material and methods: We examined 184 children with CHD after radical correction (mean age 9.54 ± 0.36 years) and 40 healthy children. All children underwent echocardiography by tissue Doppler studied definition of myocardial velocities in systole (S`) and during early and late diastole (E` and A`), determined by the ratio E/E`. Results: We observed a significant reduction of systolic myocardial velocities in children with CHD in all myocardial segments, namely: S`mv 7.81 ± 0.10 cm/s; S`ivs 6.54 ± 0.07 cm/s; S`mv 9.70 ± 0.12 cm/s (p < 0.01), which distinguishes them from indicators of healthy children between 21.25% and 31.96%. The value of the ratio E/E` exceeds parameters in healthy children by 20.75% for the left ventricle and to 35.36% for the right ventricle and was 7.45 ± 0.21 and 6.42 ± 0.14 respectively (p < 0.01). The ratio E/E` for right ventricle exceeds indicators of healthy children by 25.2% in the pre-clinical stage of heart failure. Conclusions: According to the tissue Doppler in children with CHD, radical correction results in reduction of longitudinal myocardial contractility and relaxation disorder.