How Long Can You Have Pulmonary Embolism Without Knowing?

A pulmonary embolism (PE) is a blood clot that blocks a blood vessel in your lungs. It is a serious condition that can be life-threatening. The question of how long you can have one without knowing is common, and the answer is not simple. Some people have a PE with no symptoms at all. Others have mild symptoms that they mistake for a cold, a pulled muscle, or simply feeling tired. In other cases, the first sign of a PE is sudden collapse or death. The truth is, you can have a pulmonary embolism for days or even longer without recognizing it, but this is not a situation where waiting to see if you feel better is safe. Any suspicion of a PE requires immediate medical evaluation.

What Exactly Is a Pulmonary Embolism?

A pulmonary embolism happens when a blood clot travels from somewhere else in your body—usually a deep vein in your leg—and lodges in an artery in your lung. This blockage stops blood from reaching parts of the lung tissue. When lung tissue does not get blood, it cannot oxygenate your blood properly.

The medical term for the leg clot is deep vein thrombosis (DVT). The DVT itself may cause leg pain, swelling, or warmth. Or it may cause nothing at all. When part of that clot breaks off and moves to the lungs, it becomes a PE. The size of the clot and your overall health determine how severe the symptoms are.

Small clots may block only a tiny portion of the lung. Large clots can block the main artery leaving the heart, which is often fatal within minutes to hours. This range of severity is why the condition is so dangerous—it can be barely noticeable or instantly overwhelming.

How Long Can You Have Pulmonary Embolism Without Knowing?

You can have a pulmonary embolism without knowing for days, weeks, or in rare cases, even longer. The key factor is the size and location of the clot. A small clot in a peripheral part of the lung may produce no symptoms at all. Your body may slowly break it down on its own without you ever being aware it happened.

However, “without knowing” does not mean “without risk.” Even a silent PE damages lung tissue and puts strain on your heart. The danger is that a small clot today can be followed by a larger, more dangerous clot tomorrow. You cannot predict which clot will be the one that causes severe harm.

If you have symptoms at all, even mild ones, you should not assume they are harmless. Shortness of breath, chest pain, or a cough that does not go away deserve a medical workup, especially if you have risk factors for blood clots.

What Are the First Signs of a Pulmonary Embolism?

The most common symptoms of a PE are sudden shortness of breath, chest pain that worsens with deep breathing, and a rapid heart rate. Some people also cough up blood. Others feel lightheaded or faint. These symptoms can come on suddenly or develop gradually over days.

The tricky part is that these symptoms overlap with many other conditions. Shortness of breath can be from anxiety, a respiratory infection, or heart problems. Chest pain can be from muscle strain or acid reflux. This overlap is why PEs are frequently missed in the early stages.

A specific pattern that raises suspicion is a combination of symptoms. If you have leg swelling or pain on one side, plus new shortness of breath or chest pain, that combination is more concerning than either symptom alone. This pairing points toward a clot that started in the leg and moved to the lung.

Who Is at Risk for a Silent Pulmonary Embolism?

Certain people are at higher risk for developing blood clots that can become PEs. Knowing your risk level helps you decide how seriously to take mild symptoms.

• Recent surgery or injury — especially hip, knee, or abdominal surgery. Immobility during recovery slows blood flow in the legs.
• Prolonged immobility — long car rides, plane flights, or bed rest. Blood pools in the legs when muscles are not moving.
• Cancer — certain cancers and their treatments increase clotting risk.
• Pregnancy and the postpartum period — hormonal changes and pressure on pelvic veins raise risk.
• Hormonal medications — birth control pills and hormone replacement therapy containing estrogen.
• Smoking — damages blood vessels and increases clotting tendency.
• Obesity — increases pressure in leg veins and reduces mobility.
• Family history of blood clots — inherited clotting disorders like Factor V Leiden.
• Age over 60 — risk rises with age, though younger people can still get clots.

Having one or more of these risk factors does not mean you will get a clot. But it does mean that new respiratory symptoms should be taken more seriously. The more risk factors you have, the lower your threshold should be for seeking medical attention.

Why Is a Silent Pulmonary Embolism Dangerous?

A PE that produces no symptoms is still dangerous for two main reasons. First, it damages lung tissue. The blocked artery means that part of the lung does not get oxygen. Over time, this can cause scarring and permanent reduction in lung function.

Second, a silent PE can be a warning sign. If you formed one clot, you are at higher risk of forming another. The next clot could be larger. It could block a bigger artery. It could be fatal.

There is also the risk of developing chronic thromboembolic pulmonary hypertension (CTEPH). This is a condition where repeated or large PEs cause high blood pressure in the arteries of the lungs. It develops over months to years and can lead to heart failure if untreated. Some people who had “silent” PEs are later diagnosed with CTEPH when they develop progressive shortness of breath.

This is why doctors do not take even a suspected PE lightly. The diagnostic tests—a CT scan of the chest or a ventilation-perfusion (VQ) scan—are ordered quickly when a PE is suspected. The treatment, usually blood thinners, is started immediately because the risk of another clot is highest in the first weeks after the first one.

What Happens If a Pulmonary Embolism Goes Untreated?

Untreated PE has a high mortality rate. Studies consistently show that a significant percentage of untreated PEs are fatal. The most dangerous period is the first hour to several hours after the clot reaches the lungs, when the heart may not be able to pump blood against the blockage.

If you survive the initial event, the clot may partially dissolve on its own. But the risk of a second, larger clot remains. The standard treatment with blood thinners reduces the risk of death dramatically. This is why treatment is started before the diagnosis is fully confirmed in many cases—the risk of waiting outweighs the risk of treating.

After the acute danger passes, the long-term risks remain. Lung function may be permanently reduced. The heart may be weakened. You may develop chronic breathlessness that limits your daily activities. Early treatment reduces these risks substantially.

Can a Pulmonary Embolism Resolve on Its Own?

Yes, the body can dissolve a small PE on its own. The blood has natural mechanisms to break down clots. Over weeks to months, the body’s fibrinolytic system can clear even a moderate clot from the lung.

But this is not a reason to avoid treatment. You cannot know whether your clot is small enough to resolve safely. You cannot know whether another clot is forming. And even a clot that resolves leaves behind some damage to the blood vessel wall and lung tissue.

Some research suggests that up to half of all PEs are “silent” and may never be diagnosed. Many of these resolve without medical intervention. But the ones that do not resolve, or the ones that are larger than they appear, are what make PE a leading cause of preventable death in hospitalized patients.

When Should You Seek Immediate Medical Care?

If you have any of the following symptoms, you should go to an emergency department immediately:

• Sudden shortness of breath that does not improve with rest
• Chest pain that worsens with deep breathing or coughing
• Coughing up blood
• Fainting or feeling like you might faint
• Rapid heart rate with no clear cause

These symptoms can indicate a large PE that is putting your life at risk. Do not wait to see if they pass. Do not try to treat them at home. Call emergency services or have someone drive you to the hospital.

If you have milder symptoms that persist, such as a lingering cough, mild breathlessness with exertion, or unexplained fatigue, see your doctor within a day or two. Mention any risk factors you have for blood clots. Ask specifically whether a PE could be the cause.