Abstract Introduction: MDCT pulmonary angiography is the method of choice for the detection of pulmonary embolism (PE). The severity of PE as estimated by the obstruction index (OI) and right ventricular dysfunction (RVD) can be evaluated with MDCT. Objective:To investigate the correlation between the OI, RVD and clinical presentation in patients with acute PE. Methods:Among 70 patients with suspected PE, 35 patients proved to have PE with MDCT. The CT OI and the RV/LV diameter (RVD-ratio) using the four-chamber view of the heart were calcu-lated for PE patients. The cut-off for the OI to detect RVD was constructed using ROC curve. Results:Dyspnea and RVD (RVD-ratio >1) were significantly more common in patients with central pulmonary emboli. The mean OI (35%± 19%) was significantly higher in patients with dyspnea, tachycardia and obesity. A positive correlation was found between the OI and both the CT pulmonary artery diameter (r= 0.66,p 0.001) and the RVD-ratio (r= 0.628,p 0.001). The mean OI was significantly higher in patients with RVD (p 0.001). A CT OI > 43% identified more than 90% of patients with RVD (area under the curve on ROC analysis: 0.825;p 0.001). Conclusion:The mean OI correlated linearly with PA diameter and RVD-ratio. OI > 43% proved to be an independent predictor of RVD.