Patients admitted to the intensive care unit (ICU) with pulmonary embolism (PE) usually have an increased mortality risk. This risk can be estimated by the Pulmonary Embolism Severity Index (PESI), composed of clinical features such as tachycardia, tachypnoea, hypotension, altered mental status and decreased arterial oxygen saturation. Patients with persistent hypotension (systolic blood pressure <90 mmHg for ≥15 min) carry the highest mortality risk and in the absence of contraindications, international guidelines recommend to treat these patients with fibrinolysis. Choosing the best anticoagulation strategy for patients with acute PE can be difficult, especially in patients with severe obesity and those with contraindications to anticoagulation. Although the guidelines suggest that intermittent subcutaneous and continuous intravenous anticoagulant treatment are equally effective, the intermittent subcutaneous treatment does not warrant continuous protection against clinical deterioration. To illustrate this problem, we present two cases of patients with severe PE admitted to the ICU. © 2017, Nederlandse Vereniging voor Intensive Care. All rights reserved.