Embolism
Obstruction of a blood vessel by material that has travelled there from elsewhere in the circulation.
What it means
An embolism occurs when material carried in the bloodstream lodges in a vessel too narrow to admit it, obstructing flow beyond that point. The travelling material is an embolus.
The distinction from thrombosis is one of origin: a thrombus forms where it sits, whereas an embolus forms elsewhere and travels.
Most emboli are fragments of blood clot, but other types occur:
- Pulmonary embolism — clot reaching the lung arteries, usually from a leg vein
- Fat embolism — following major long bone fracture
- Air embolism — following certain procedures or diving injury
- Septic embolism — infected material, as in endocarditis
In practice
Most frequently as pulmonary embolism, investigated with a D-dimer and CT pulmonary angiogram, and as a cause of stroke where clot travels from the heart to the cerebral circulation.
Atrial fibrillation predisposes to this by allowing clot to form in the fibrillating atrium, which is why anticoagulation is offered.
Why it matters
Pulmonary embolism is a medical emergency, presenting with breathlessness, pleuritic chest pain, coughing blood, a rapid heart rate or collapse. It can be fatal and is highly treatable when identified.
The possibility should be considered in anyone with these symptoms following surgery, immobility, long-haul travel, pregnancy or with active cancer.
Clinically reviewed by Dr Mohammad Zubair Khan, GMC 7563469
Last reviewed
August 30, 2026