A 73-year-old woman complaining of increased dyspnea, but no shock, was admitted under an echographic diagnosis of right atrial tumor. Echo-cardiogram at the time of admission did not reveal the right atrial tumor, and a massive pulmonary embolus was detected a pulmonary arteriography. After the infusion of tissue plasminogen activator and heparin, pulmonary arterial systolic pressure was decreased from 66 to 43mmHg, and dyspnea was improved. However, repeated pulmonary arteriograms showed no change of the pulmonary embolus, thus emergency pulmonary embolectomy was indicated. Massive thrombi, which were suspected to have moved from the lower extremities, were successfully removed. During operation, the following critical events were encountered; shock during IVC taping and severe hypoxia immediately after the pulmonary revascularization. These problems were successfully controlled by partial extracorporeal circulation. Pulmonary pressure decreased to 25mmHg postoperatively and she is doing well with anticoagulant therapy.