Pulmonary Embolism Usually Begins as a Clot in the Leg

A blood clot in your leg doesn’t always stay in your leg. Sometimes it breaks loose, travels through the bloodstream, and lodges in an artery of the lungs — that’s a pulmonary embolism. Most often, the clot starts in the legs or pelvis.

It can turn serious fast. The good news? When it’s diagnosed and treated promptly, the outcome is often good — and treatment also helps stop new clots from forming.

Overview

In a pulmonary embolism, one or more arteries in the lungs become blocked — most often by a blood clot. That clot usually forms in a deep vein of the leg or pelvis before travelling through the bloodstream to the lungs, which is why we see it so closely linked to deep vein thrombosis (DVT).

The effects of pulmonary embolism depend on the size and number of clots, how much of the lung circulation is blocked, and the person’s overall heart and lung health. Small clots may cause mild or even vague symptoms, while larger clots can strain the heart and reduce oxygen levels. Because of this range, pulmonary embolism may be mistaken for other conditions unless it is carefully evaluated.

Yes, it can be life-threatening — but we can treat it effectively. What matters most is recognizing it early, getting assessed urgently when warning symptoms appear, and following a plan that lowers your risk of complications or another clot down the line.

How pulmonary embolism affects the body

The lungs receive blood from the right side of the heart through the pulmonary arteries. When a clot blocks one of these arteries, blood flow to part of the lung is reduced or cut off. This can interfere with oxygen exchange and make breathing feel difficult or uncomfortable.

If the blockage is large, the right side of the heart must work harder to push blood through the narrowed lung circulation. In some people, this can lead to low blood pressure, dizziness, or collapse. Smaller clots may not cause immediate severe instability, but they can still damage lung tissue or cause recurring symptoms.

No two clots behave exactly the same. Some people have a sudden, obvious event; others have symptoms so subtle they’re easy to miss. That’s why we look at the whole picture — your symptoms, recent travel or surgery, cancer history, pregnancy status, medications, and any signs of DVT.

Symptoms and warning signs

Symptoms of pulmonary embolism often begin suddenly, but they can also develop over hours or days. The most common symptoms are shortness of breath, chest pain, and a fast heart rate. The chest pain may feel sharp and may become worse with deep breathing, coughing, or movement.

Other possible symptoms include cough, coughing up blood, lightheadedness, fainting, anxiety, sweating, or a feeling of being unwell without a clear cause. Some people also notice symptoms in a leg before the lung clot is found, such as swelling, warmth, tenderness, or redness in one calf or thigh.

These symptoms can look a lot like pneumonia, asthma, heart problems, or even a panic attack. So please — don’t brush off unexplained shortness of breath or chest pain, especially if you have risk factors for clots.

• Sudden shortness of breath
• Chest pain, especially with deep breaths
• Rapid heartbeat
• Cough, sometimes with blood
• Fainting or near-fainting
• One-sided leg swelling or pain

Causes and risk factors

Most pulmonary emboli come from clots that form in the deep veins of the legs or pelvis. These clots are more likely to develop when blood flow slows down, the blood is more prone to clotting, or the lining of a blood vessel is injured. Doctors often think about these clotting triggers together when assessing a patient’s risk.

Risk factors include recent surgery, hospitalization, prolonged bed rest, long-distance travel, major injury, pregnancy and the weeks after delivery, smoking, obesity, increasing age, and hormone-related medications such as some birth control pills or hormone therapy. Certain chronic illnesses, especially cancer and heart or lung disease, can also increase risk.

Some people have inherited or acquired conditions that make the blood clot more easily. A previous DVT or pulmonary embolism is one of the strongest predictors of another event. In a smaller number of cases, a clear cause is not found, but treatment and prevention still remain important.

Doctors may also evaluate for related vascular conditions when appropriate, especially if symptoms overlap with varicose veins or chronic venous problems, though these are not the same as DVT or pulmonary embolism.

How doctors diagnose pulmonary embolism

Diagnosis starts with a medical history and physical examination. A doctor asks about symptoms, prior clots, recent immobility, surgery, travel, pregnancy, medications, cancer history, and family history of clotting disorders. They also check vital signs, oxygen levels, and the legs for signs of DVT.

Because symptoms can mimic many other conditions, doctors often use clinical assessment tools to estimate how likely pulmonary embolism is before ordering tests. Blood testing may include a D-dimer test, which can help rule out a clot in selected lower-risk patients. If pulmonary embolism is still suspected, imaging is usually needed.

The most commonly used imaging test is CT pulmonary angiography, which can show a clot in the lung arteries. Some patients may have a ventilation-perfusion scan instead, especially when CT contrast is not suitable. Ultrasound of the legs may help detect DVT, and an echocardiogram may be used if there is concern about strain on the heart. In some cases, advanced imaging and coordinated care with interventional radiology specialists may be part of the evaluation and treatment plan.

Treatment options

The main treatment for pulmonary embolism is anticoagulation, often called blood-thinning treatment. These medicines do not dissolve an existing clot immediately, but they help prevent the clot from growing and reduce the risk of new clots while the body gradually breaks down the blockage. The type of medication and length of treatment depend on the patient’s risk factors, the severity of the embolism, and whether the clot was provoked by a temporary event.

For people who are hemodynamically unstable or have a large pulmonary embolism causing significant strain on the heart, emergency treatment may be needed. This can include clot-dissolving medicines or procedures to remove or break up the clot. In selected cases, minimally invasive approaches such as angiography-guided catheter-based treatment may be considered by experienced teams.

If blood thinners are not possible because of a high bleeding risk, some patients may need a filter placed in the large vein that returns blood from the lower body to the heart. This is used selectively and does not replace treatment of the underlying clotting tendency. Supportive care may include oxygen, pain control, and close monitoring in the hospital.

Some patients also need evaluation for underlying cardiovascular or rhythm issues that may affect recovery. Depending on the broader picture, care may involve specialists in cardiology, pulmonology, hematology, and vascular medicine.

Recovery, prevention, and self-care

Everyone recovers at their own pace. Some people feel better within days or weeks; others deal with lingering fatigue, breathlessness, or reduced stamina for longer. Keep your follow-up appointments — they’re where we review symptoms, confirm the treatment plan, and decide how long anticoagulation should continue. Take your medicines exactly as prescribed and attend monitoring visits if needed.

Preventing another clot often involves addressing risk factors. Regular movement during long trips, early walking after surgery when medically appropriate, staying hydrated, and using prescribed compression methods or preventive medications in high-risk situations can all help. Smoking cessation, weight management, and control of chronic conditions may also lower future risk.

If you’ve had a pulmonary embolism, tell your healthcare team before surgery, pregnancy, or long-distance travel so a prevention plan can be put in place. Ask about how your blood thinner interacts with other medicines, supplements, or changes in your diet. And never stop anticoagulation on your own without medical advice.

Near the end of treatment or during follow-up, some people may need reassessment for ongoing breathlessness or rare complications such as chronic clot-related pressure changes in the lung circulation. Multidisciplinary evaluation can help guide next steps. Acıbadem Health Point’s multidisciplinary specialists and JCI-accredited hospitals also diagnose and treat pulmonary embolism for international patients when coordinated specialist care is needed.

When to seek medical care

Don’t wait if you notice symptoms that could suggest pulmonary embolism. Seek emergency care right away for sudden shortness of breath, chest pain, coughing up blood, fainting, severe dizziness, or a rapidly worsening heartbeat. These don’t always mean a lung clot — but they need to be checked without delay.

Medical advice should also be sought promptly for possible DVT symptoms such as one-sided leg swelling, calf pain, warmth, or redness, especially after surgery, a long trip, or a period of bed rest. Early treatment of DVT can reduce the chance of a clot reaching the lungs.

Anyone already taking blood thinners should contact a doctor urgently if they have signs of significant bleeding, black stools, vomiting blood, severe headache, a serious fall, or unusual bruising. Follow-up care matters just as much as emergency treatment, because it helps reduce the risk of recurrence and supports a safer recovery.

Frequently asked questions