Two names, one disease
When blood clots inside a deep vein — most often in the calf or thigh — that is a deep vein thrombosis (DVT). If a piece of that clot breaks off and is carried up through the veins, through the right side of the heart, and lodges in the lung's arteries, that is a pulmonary embolism (PE). Because they are really two ends of the same process, doctors group them under one umbrella term: venous thromboembolism (VTE).
The key insight is the direction of flow. Veins drain toward the heart, so anything loose in a leg vein travels upward. The right heart pumps that blood straight into the lungs to pick up oxygen. So the lung is the first fine filter the bloodstream meets — which is exactly why leg clots end up there rather than in the brain or kidneys.
What goes wrong when a clot arrives
A clot blocks a pulmonary artery, so blood can no longer reach the air sacs downstream. Those sacs are still ventilated with air but no longer perfused with blood — a classic mismatch you'll see again in this track. The body cannot pick up oxygen there, which is one reason shortness of breath is the most common symptom.
- Sudden breathlessness — often coming on over minutes to hours, sometimes at rest.
- Sharp chest pain that worsens with a deep breath — this pleuritic chest pain happens when the clot irritates the lung lining.
- A fast heartbeat or feeling faint — the heart speeds up to push blood past the blockage.
- Coughing up a little blood — hemoptysis can appear if a small piece of lung dies from lost blood supply.
If a segment of lung tissue actually dies from the cut-off blood supply, that is a pulmonary infarction. It is less common than you might expect, because lung tissue has a backup supply from the bronchial arteries — a quiet safety feature most people never know they have.