Although the effects of right ventricular (RV) volume and pressure overload (RVVO and RVPO) on ventricular septal motion are different, the differential effect on left ventricular (LV) function is still controversial. The Doppler-derived index (Tei index) combining systolic and diastolic ventricular function, defined as the sum of isovolumetric contraction time (ICT) and isovolumetric relaxation time (IRT) divided by ejection time (ET), has been demonstrated to be a useful index to estimate LV function and to predict the prognosis of patients with congestive heart failure. This study was designed to evaluate the differential effects of RVVO and RVPO on LV function using the Tei index. Study patients consisted of 26 age-matched normal subjects, 22 patients with atrial septal defect (ASD) with normal or borderline RV pressure and 25 with primary pulmonary hypertension (PPH). All subjects had normal LV ejection fractions measured with 2-dimensional echocardiogram using biplane Simpson's method (61 ± 4 vs 61 ± 4 vs 63 ± 8 %, normal vs ASD vs PPH). Tei index was easily obtained in all subjects from transthoracic Doppler echocardiogram of LV inflow and outflow. Patients with ASD had normal ICT, IRT and ET, resulting in normal Tei index, however, patients with PPH had significantly prolonged ICT and IRT with shortened ET, resulting in a significant increase in Tei index (0.38 ± 0.04 vs 0.36 ± 0.03 vs 0.61 ± 0.22, p < 0.001). Although RVVO due to ASD has no significant effects on LV function, RVPO due to PPH can adversely affect LV function. The Tei index is a simple and sensitive measure to assess LV function caused by RVVO or RVPO.