This is an investigation into the composition of pulmonary embolism (PE). PE is the third leading cause of mortality. PE affects up to 900,000 people in the USA annually with an overall mortality of 30%, if untreated, and 8% if treated. Furthermore, of the survivors, 30% have a long-term pulmonary disability from chronic thromboembolic disease (CTED) and 4-6% have pulmonary hypertension (CTEPH). The percutaneous extraction of pulmonary emboli provides an opportunity to study the thromboembolism with regard to the histologic makeup in order to determine the likelihood of spontaneous resolution with anticoagulation alone or even exogenous clot-dissolving thrombolytic medications such as tissue plasminogen activator (tPA). It has been my experience that despite long overnight infusions of thrombolytics, some PE never completely resolves. This may have profound implications for the immediate management of these patients as they present with acute PE. The administration of anticoagulants or thrombolytics, may in fact be inadequate to remove the thromboembolism, and instead, percutaneous extraction would be required to allow pulmonary blood to flow once again. In this study, we will send specimens of the thromboembolism to the lab for light and electron microscopy. We will also correlate with the imaging and medical records to identify patterns. The procedure performed on the patient will be identical to the pulmonary embolectomy procedure performed, however instead of disposing of the entire specimen, a portion will be submitted for this investigation. There will be no additional patient obligations or procedures other than consent. This is an initial study to characterize the extracted blood clots and analyze them with light and electron microscopy in order to determine if some clots would be insoluble to the body's intrinsic tPA or therapeutic delivery. Such information may guide future therapies in the treatment of PE and as such could have profound implications for the management of this disease.