Pulmonary embolism is the sudden blockage of a major blood vessel (artery) in the lung, usually by a blood clot. In most cases, the clots are small and aren't deadly, but they can damage the lung. But ...

Pulmonary embolism occurs when an embolus breaks away from a thrombus and blocks the pulmonary artery, generating symptoms that include shortness of breath, chest pain, fainting and haemoptysis.