Echocardiographic assessment of the right ventricular function plays an important role in diagnosis of pulmonary hypertension (PH). However, it has not been fully understood about utility of echocardiography in assessment of progressive PH. The purpose of the present study was to evaluate utility of the echocardiographic assessment of PH. One hundred and eight 12-week-old, male Sprague-Dawley rats were injected with monocrotaline (MCT) or saline solution (MCT-injected rats: n=54; saline: n=54). Serial echocardiography and right ventricular systolic pressure (RVSP) measurements via a cardiac catheter were performed. Histologic examination of the small intrapulmonary arteries at week 2 revealed pathologic vascular remodeling leading to narrowing of the vascular lumen. Tissue Doppler imaging in the MCT-injected rats showed a significant difference compared with that in the saline group at week 2. RVSP in the MCT group showed a significant increase compared with the saline group at week 4 (saline group 28.0±4.7 mmHg, MCT group 60.2±14.9 mmHg). Two-dimensional echocardiography in the MCT group showed a significant difference compared with that in the saline group at week 4. The right ventricular (RV) remodeling characterized by interstitial myocardial fibrosis was observed in the MCT group at week 6. The ratio of peak trans-tricuspid early diastolic wave velocity to active filling with atrial systolic velocity showed diastolic dysfunction in the MCT group at week 7. It is considered that echocardiographic analysis permits accurate determination of the stage of disease development in MCT-induced RV failure.