Background/Aims: We aimed to determine the effects of adenoidectomy and/or tonsillectomy (AT) on cardiac functions in children with adenoid and/or tonsillary hypertrophy and obstructive sleep apnea syndrome (OSAS) by using echocardiography with tissue Doppler imaging facility (TDI). Methods: Twenty-nine children with adenoid and/or tonsillary hypertrophy and OSAS and 26 children with primary snoring entered the study. Cardiac functions were assessed by echocardiography with TDI in both groups. Tests were repeated in the OSAS group 6 months after treatment with AT. Results: Echocardiography showed a decrease in estimated pulmonary artery systolic pressure from 31 ± 4.2 to 13.1 ± 2.3 (p < 0.001). In TDI, tricuspid Em and Em/Am increased from 11.0 ± 2.7 to 13.5 ± 2.7 cm/s (p < 0.001), and 1.46 ± 0.52 to 1.82 ± 0.53 (p = 0.004), respectively, following AT, indicating improvement in right ventricular diastolic dysfunction. Similarly, mitral Em and Em /Am increased from 12.3 ± 2.1 to 16.3 ± 2.7 cm/s, and from 1.65 ± 0.51 to 2.30 ± 0.54, respectively (p < 0.001). There was no significant difference between postoperative values and control group values. Conclusion: TDI is a technique able to detect diastolic dysfunction unnoticeable by conventional echocardiography. Following AT, we observed improvement in both left and right ventricular diastolic functions using TDI.