Abstract： Objective To prospectively assess right ventricular dysfunction and the metergasis before and after therapy of thrombolysis with ECG gated multi-detector spiral computed tomography (MSCT)in patients with acute pulmonary embolism. Methods Triple rule-out ECG gated MSCT examination was performed in 96 consecutive patients suspected of PE. 25 patients with central PE were confirmed. 25 agematched subjects without cardiac and pulmonary disease were recruited as control group. Triple rule-out ECG gated MSCT were performed again to assess cardiac function after therapy of thrombolysis. Dimension ratios for the right ventricle (RV) and left ventricle ( LV), main pulmonary artery and aorta were measured.Furthermore, the RV and LV end-diastolic volumes (EDV), end-systolic volume (ESV) and ejection fraction (EF) were also measured. The mean values were compared with analysis of variance (ANOVA) and Newman-Keuls test before and after thrombolysis. Results The mean values of RVEDV, RVESV, RVEF,RV/LV ESV volume ratio, RV/LV dimension ratio and main pulmonary artery/aorta dimension ratio in control group were (150.5±24.1) ml,(71.5 ±18.5) ml, (53.5 ±4.2)%, 1.08 ±0.04, 1.01 ±0.04 and 0. 99 ±0. 02, respectively. While those in PE group were ( 190. 3 ± 16. 2) ml, ( 128. 1 ± 13.2) ml,(32.7 ± 3.6 ) %, 2.00 ± 0.26, 1.30 ± 0. 09 and 1.34 ± 0. 11, respectively. Those after therapy of thrombolysis were ( 159. 2 ± 21.5 ) ml, ( 80. 7 ± 9.4) ml, (49. 2 ± 5.9) %, 1.22 ± 0.25, 1.02 ± 0.02 and 1.02±0.11,respectively. ESV and EDV of RV were larger (q= 6.28, P<0.01; q=7.59, P<0.01),EF value was lower (q = 4. 82, P < 0.01 ) in PE group than those in control group. RV/LV ESV volume ratio, the RV/LV dimension ratio and main pulmonary artery/aorta dimension ratio were larger ( q = 6. 04,P <0. 01; q =4. 43, P <0. 01; q =4. 36, P <0. 01 ) and EDV of LV was lower in PE group than those in control group. However, ESV and EDV of RV and RV/LV ESV volume ratio were lower (q = 5.03, P <0.01;q=6. 11,P<0.01;q=4.74,P<0.01), EF value was larger (q=6.29, P<0.01) and EDV of LV was larger(q =4.01 ,P <0.01 ) after therapy of thrombolysis than before. Conclusion Retrospective triple rule-out ECG-gated MSCT can show pulmonary embolism, measure the function of RV and LV and evaluate curative effect of thrombolysis.