In selected patients with acute pulmonary embolism(PE), low dose (50mg/2h) recombinant tissue plasminogen activator (rt-PA) regimen had been reported to have less bleeding tendency than the FDA-approved rt-PA 100mg/2h regimen 100mg/2h regimen (3% vs.10%), it is worthwhile to reveal whether low dose rt-PA plus low molecular weight heparin (LMWH) can rapidly reverses RV pressure overload in PE, but not increase bleeding and other adverse events. The aim of the study is to compare thrombolytic treatment with LMWH in patients with acute normotensive PE with right ventricular dysfunction(RVD).