BACKGROUND The aim of this study was to evaluate the feasibility of an R-wave modified tissue Doppler imaging (TDI) myocardial performance index (MPI), or MPI TDI-R, for the assessment of cardiac function in children with congestive heart failure (CHF). MATERIAL AND METHODS Forty children with CHF and 40 normal children were evaluated using the modified pediatric Ross heart failure grading system. TDI recorded the spectrum of diastolic function at the mitral valve annulus to measure the MPI. Twelve-lead electrocardiogram (ECG) measured the R-wave in the QRS complex, resulting in the modified MPI TDI-R. Correlation between the MPI TDI-R, other echocardiographic indices, and the Ross heart failure grades were analyzed, with reproducibility analysis. RESULTS Compared with normal children, the MPI TDI and MPI TDI-R were significantly increased in the pediatric CHF group (P<0.01). The MPI TDI-R was significantly correlated with other indices of cardiac function and Ross grading for CHF in children (r=0.769). The MPI TDI-R showed good correlation with the findings of the MPI TDI, calculated by traditional methods. Receiver-operating characteristic (ROC) curve analysis showed that the MPI TDI-R had a sensitivity of 67.5%, and a specificity of 97.5%. The reproducibility of the MPI TDI-R was confirmed to be superior when compared with the non-modified MPI TDI. CONCLUSIONS This feasibility study showed that the modified MPI TDI-R, formed by combining the MPI TDI with synchronous surface ECG measurements, was simple to perform, reproducible, and provided a specific index for the assessment of cardiac function in children with CHF.