The aim of this study was to evaluate the mid-term clinical status of patients following tetralogy of Fallot (TOF) repair. We performed a cross-sectional observational analysis of 57 postoperative TOF patients and 58 age-matched controls. Patients were examined with myocardial performance index (MPI), which was obtained by tissue Doppler imaging (TDI) in addition to the conventional methods. Compared with controls, patients had significantly higher right ventricular (RV) dimensions and volumes, RV MPI and left ventricular (LV) MPI, and significantly lower RV ejection fraction (EF), LV EF, exercise duration, and maximum heart rate with exercise (p<0.001 for all parameters). A positive correlation was found between RV MPI and LV MPI (r=0.541, p<0.001). There was a negative correlation between LV MPI and exercise duration (r=0.260, p=0.034). After total surgical correction of TOF, the patients had a good clinical status at the mid-term follow-up; decreased exercise capacity and impaired functions in both ventricles related to the degree of pulmonary regurgitation were found. By using MPI, impaired cardiac functions can identify such conditions before they become clinically symptomatic.