RISK STRATIFICATION OF PULMONARY THROMBOEMBOLISM The prognosis of pulmonary thromboembolism (PET) is related to the cardiopulmonary reserve of the patient and the magnitude of the embolus that impacts pulmonary circulation. The presence of hemodynamic instability (shock) stratifies a group of patients with high mortality, which should be treated with thrombolysis. Patients without shock but with right ventricular dysfunction can have a dismal evolution and should be managed aggressively. CAT scan, echocardiography and serum markers can be of value to define patients with a higher mortality. The available evidence to define the best diagnostic and therapeutic strategy is scanty, controversial and inconclusive. A good combination of clinical, imaging and biological markers should be defined to identify those patients without shock but with a high rate of complications and mortality, that could benefit from aggressive treatments.