Despite recent introduction of catheter-based invasive strategy, the mainstay of the treatment for acute pulmonary thromboembolism is antithrombotic medication. The most standard tactics is to start intravenous unfractionated heparin (for a better substitute, low-molecular-weight heparin is available overseas), and to shift it to oral warfarin and maintain for at least 3 months. The duration of prophylactic anticoagulation may be extended longer by weighing the risks of recurrence and anticoagulant-related bleeding. Use of fibrinolytic agents should be considered first of all in patients who have hemodynamic instability or cardiogenic shock (massive type), because its effects are rapid and drastic in many cases. Recent evidence suggests that fibrinolytic therapy be also effective in patients with right ventricular pressure overload and dysfunction (sub-massive type).