A blood clot can reach the lungs very quickly once it breaks away from a deep vein in the leg. The exact travel time has not been measured reliably, but available information suggests the journey may take seconds to minutes.
The larger uncertainty is when the clot will detach. A clot may remain in the leg for days or weeks before breaking loose, and newly formed clots appear more likely to travel during the first few weeks. This means there is no dependable countdown that can predict when a pulmonary embolism will happen.
Symptoms may begin suddenly after the clot reaches and blocks an artery in the lungs. Warning signs can include sudden shortness of breath, chest pain, fainting, or a rapid worsening of breathing. These symptoms should be treated as an emergency, especially when accompanied by possible signs of a clot in the leg.
Call emergency services or go to the nearest emergency department immediately if a pulmonary embolism is suspected. Do not wait for symptoms to improve or try to treat a possible blood clot with medication on your own.