Background:The use of thrombolytic agents in the treatment of hemodynamically stable patients with acute submassive pulmonary embolism remains controversial. Materials and Methods:20 patients were enrolled as acute submassive pulmonary embolism.They had pulmonary hypertension and right ventricular dysfunction (RV hypokinesia & dilatation)by echocardiography but had no systemic hypotension or shock.10 patients were treated with heparin only and the other 10 patients treated with rt-PA plus heparin.Primary end point was time(hours) of symptom relief including recovery of vital sign and echocardiography follow up for RV function and RV systolic pressure two weeks later after treatment.Secondary end points were death,recurrent embolism,secondary thrombolysis,embolectomy and major beeding.We also compared biochemical makers including D-dimer antithrombin III and protein C/S in both groups. Results:With respect to primary end points,rt-PA group had reduced times of symptom relief than heparin only group(p=0.013),and both groups showed good RV dysfunction improvement similary(p=0.22).With respect to secondary end points, both groups have no remarkable difference and only one patient in heparin group received embolectomy. Conclusion:When given in conjunction with heparin, rt-PA can shorten the clinical course of patients who have acute submassive pulmonary embolism than heparin only group.