Persistent pulmonary hypertension of the newborn is a clinical syndrome associated with a variety of cardiopulmonary diseases. Serial evaluation of pulmonary circulation and cardiac function is important, but available imaging techniques have been limited. A new Doppler index combining systolic and diastolic time intervals (the Tei index, which is a simple and noninvasive measurement) has been reported to be useful for the assessment of global cardiac function in adults and children. The purpose of this study was to test the effectiveness of the Tei index in prospectively assessing ventricular function and pulmonary circulation in a newborn piglet model with hypoxic pulmonary hypertension. One-day-old piglets (1.1-1.6 kg) were intubated and prepared for the experiments under room air and hypoxia. A complete two-dimensional Doppler echocardiographic examination was performed. Common hemodynamic variables were measured continuously throughout the study. The right ventricle (RV) Tei index under hypoxia (fraction of inspired oxygen ϭ 0.10) was significantly higher than the value under air ventilation (medians, 0.38 versus 0.56; p Ͻ 0.05). Moreover, there was a significant correlation between RV Tei index and mean pulmonary artery pressure and positive linear correlation between individual changes in RV Tei index and changes in mPAP (r 2 ϭ 0.799, p Ͻ 0.05). We conclude that the Tei index is useful for assessing the function of the RV and the left ventricle and pulmonary circulation in a newborn piglet model with hypoxic pulmonary hypertension. These results suggest that the Tei index will become an objective method of assessing patients with persistent pulmonary hypertension of the newborn. Abbreviations PPHN, persistent pulmonary hypertension of the newborn RV, right ventricle LV, left ventricle PAP, pulmonary artery pressure HR, heart rate mPAP, mean pulmonary artery pressure SBP, systemic blood pressure mSBP, mean systemic blood pressure CVP, central venous pressure TR, tricuspid regurgitation PDA, patent ductus arteriosus PFO, patent foramen ovale ROC, receiver-operating characteristic RVPEP/RVEP, right ventricular preejection period/right ventricular ejection period Persistent pulmonary hypertension of the newborn (PPHN) is a clinical syndrome associated with a variety of cardiopulmonary diseases. Infants with PPHN are severely hypoxemic owing to a sustained elevation in pulmonary vascular resistance [and the resulting elevated pulmonary artery pressure (PAP)], with associated extrapulmonary shunting (1, 2). PPHN can be associated with a myriad of clinical conditions, such as meconium aspiration, asphyxia, and heart failure. Thus, serial evaluation of pulmonary circulation and cardiac function is important to assess accurately the clinical course, the efficacy of treatment, and the prognosis. The available imaging techniques have been limited, but a new Doppler echocardiographic index combining systolic and diastolic time intervals (the Tei index) has been reported to be useful for the assessment of global funct...