Objective: The diagnosis of right ventricular myocardial infarction (RVMI) accompanied by acute inferior myocardial infarction (MI) is still a problem that we encounter. This study was designed to find out the usefulness both of peak myocardial systolic velocity (8m) and of the myocardial performance index (MPI) of the right ventricle measured by pulsed-wave tissue Doppler imaging (TDI) in assessing right ventricular function. Methods: Sixty patients who experienced a first acute inferior MI (mean [± 8D] age, 57 ± 9 years) were prospectively assessed. An ST-segment elevation of ≥ 0.1 mV in V4-V6R lead derivations was defined as an RVMI. From the echocardiographic apical four-chamber view, the Sm, the peak early diastolic velocity, peak late diastolic velocity, the ejection time, the isovolumetric relaxation time, and the contraction time of the right ventricle were recorded at the level of the tricuspid annulus by using TDI. Then, the MPI was calculated. The patients were classified into the following three groups, according to the localization of the infarct-related artery (IRA) detected using coronary angiography: group I, proximal right coronary artery; group II, distal right coronary artery; and group III, circumflex coronary artery. Results: RVMIs were detected in sixteen patients, and the IRA in 27 patients was the proximal right coronary artery. The right ventricular Sm was observed to be significantly low in patients with RVMIs and those in group I compared to those without RVMIs and those in groups II and III (10.9 ± 1.3 vs 14.3 ± 3.2 cm/s, respectively [p < 0.001]; 11.5 ± 2.5 vs 15.1 ± 3 cm/s, respectively; and 14.9 ± 2.6 cm/s, respectively [p < 0.001]). In the diagnosis of RVMI, the values for sensitivity, specificity, negative predictive value, and positive predictive value of Sm < 12 cm/s were 81%, 82%, 92%, and 62% respectively, and in the diagnosis of the proximal right coronary artery as the IRA, those values were 63%, 88%, 74%, and 81%, respectively. The MPI was high in the same patient groups (0.83 ± 0.12 vs 0.57 ± 0.11 in those patients without RVMI, respectively, [p < 0.001]; 0.74 ± 0.13 vs 0.56 ± 0.15 in group II and 0.54 ± 0.07 in group III, respectively [p < 0.001]). The sensitivity, specificity, negative predictive value, and positive predictive value of an MPI of > 0.70 in the diagnosis of RVMI were calculated as 94%, 80%, 97%, and 63%, respectively, and in the diagnosis of the proximal right coronary artery as the IRA, those values were 78%, 91%, 83%, and 88% respectively. Conclusions: An Sm <12 cm/s and an MPI > 0.70 obtained by TDI may define RVMI concomitant with acute inferior MI, and the IRA.