Previous studies showed that subclinical hypothyroidism (SH) was associated with cardiovascular disorders, such as endothelial dysfunction, atherosclerosis and myocardial dysfunction. Only one study investigated left ventricular (LV) function using pulsed tissue Doppler echocardiography (TDE) in patients with SH. However, no study has used this technique in the identification of right ventricular (RV) function in these patients. We aimed to investigate the effect of SH on RV and LV function using TDE technique. The present study included 36 newly diagnosed SH patients and 28 healthy controls. For each subjects, serum free T-3 (FT3), free T-4 (FT4), total T-3 (TT3), total T-4 (TT4), TSH, peroxidase antibody (TPOab) and thyroglobulin antibody (TGab) levels were measured, and standard echocardiography and TDE were performed. In patients with SH, TSH levels were significantly higher, and TPOab and TGab levels were significantly higher when compared to healthy controls. TDE showed that the patients had significantly lower early diastolic mitral and tricuspid annular velocity (Ea) and early/late (Ea/Aa) diastolic mitral and tricuspid annular velocity ratio (p < 0.05, p < 0.05 and p < 0.001, p < 0.001, respectively), and significantly longer isovolumetric relaxation time (IRT) of left and right ventricles (p < 0.001 and p < 0.001, respectively). However, Aa, Sa, and isovolumetric contraction time (ICT) and ET (ejection time) of left and right ventricle did not significantly differ (p=ns for all). In addition, a negative correlation between TSH and TD-derived tricuspid Ea velocity and Ea/Aa ratio, and a positive correlation between TSH and IRT of right ventricle were observed. Our findings demonstrated that SH is associated with impaired RV diastolic function in addition to impaired LV diastolic function.