In this prospective, multicenter, randomized, control study, we compare low dose rt-PA plus LMWH vs. LMWH alone in acute normotensive pulmonary embolism patients with RV dysfunction. The primary efficacy outcome is the composite of death from any cause or treatment failure, improvements of right ventricular functions on echocardiogram and pulmonary artery obstruction on CT angiographs within 7 days of randomization. Second efficacy outcome is the recurrence of pulmonary embolism and deep venous thrombosis. Safety outcomes include serious life threatening bleeding such as cerebral hemorrhage and other major bleeding episodes, also include mild bleeding. In addition, 90-day clinical and echocardiographic follow-up will be performed, the recurrence of pulmonary embolism and deep venous thrombosis will be recorded. The study is expected to enroll approximately 460 patients.