Blood clots in the heart have various causes, such as an irregular heartbeat and damage to coronary artery walls. Blood clots can cause serious symptoms and may require immediate medical intervention.

Excessive blood clotting can have many causes and can lead to reduced or blocked blood flow. This can damage organs and lead to serious health conditions.

This article discusses possible causes of blood clots in the heart, symptoms, and risk factors. It also outlines treatment options and the outlook for people with a blood clot in the heart.

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Elena Saurius & Dani Rex/Stocksy United

Blood clots develop when structures within the blood thicken and clump together into a semi-solid mass. Scientists know that three main factors contribute to this process:

  • damage to the endothelium (an inner layer of cells within blood vessels)
  • an increased tendency for blood to clot
  • a decrease in blood movement within a blood vessel

Thrombosis is the name for a blood clot (“thrombus”) that forms inside a blood vessel. Sometimes, blood clots form in the heart’s arteries. This is called coronary artery thrombosis. However, some blood clots can originate from within the heart itself.

A 2023 review notes that atrial fibrillation (AFib) is a significant cause of blood clots. With AFib, an individual’s atria, the heart’s two upper chambers, beat irregularly. This means blood can stagnate within them, eventually forming a clot.

Having risk factors for blood clots increase a person’s risk of experiencing blood clots. However, the risk factors do not necessarily cause them.

The American Heart Association (AHA) provides the following list of blood clot risk factors.

Acquired risk factors

These risk factors relate to people’s lifestyles, behaviors, or health events. They include:

Genetic risk factors

Other blood clot risk factors can pass through families. People may have a genetic risk of blood clots if they have the following:

  • a family history of blood clots
  • a personal history of multiple blood clots before the age of 40 years old
  • a personal history of unexplained miscarriage

Other risk factors

Having certain health conditions can also increase the risk of blood clots. These include:

Read more about the risk factors for developing blood clots.

A blood clot in the heart, or coronary thrombosis, may not initially cause symptoms. However, as the blood clot grows, it can obstruct a coronary artery, reducing blood flow to the heart and leading to serious heart problems.

Symptoms of coronary thrombosis include:

Coronary thrombosis can cause a heart attack. Anyone with symptoms of this condition requires urgent medical attention.

Doctors prescribe blood thinners to treat blood clots in the heart. These medications include:

Doctors sometimes recommend surgery to remove clots. One option is to widen the artery, allowing more blood to flow through it.

Learn more about treatment for blood clots.

The outlook for people with coronary thrombosis depends on the severity of the clot and how quickly they receive treatment.

A 2022 article notes that the mortality rate for coronary thrombosis in the United States is 10–12%. The rates of survival have risen in recent years.

If a blood clot travels to the brain, it can block blood flow to parts of the brain. This causes an ischemic stroke. Research shows that after a first ischemic stroke, a person has a 17% risk of death within 1 year. After multiple strokes, that figure rises to 25%.

Coronary thrombosis can lead to a heart attack. Without prompt treatment, a heart attack can be fatal. The mortality rate for heart attacks is 5–30%.

Is it a heart attack?

Heart attacks occur when there is a lack of blood supply to the heart. Symptoms include:

  • chest pain, pressure, or tightness
  • pain that may spread to arms, neck, jaw, or back
  • nausea and vomiting
  • sweaty or clammy skin
  • heartburn or indigestion
  • shortness of breath
  • coughing or wheezing
  • lightheadedness or dizziness
  • anxiety that can feel similar to a panic attack

If someone has these symptoms:

  1. Dial 911 or the number of the nearest emergency department.
  2. Stay with them until the emergency services arrive.

If a person stops breathing before emergency services arrive, perform manual chest compressions:

  1. Lock fingers together and place the base of hands in the center of the chest.
  2. Position shoulders over hands and lock elbows.
  3. Press hard and fast, at a rate of 100–120 compressions per minute, to a depth of 2 inches.
  4. Continue these movements until the person starts to breathe or move.
  5. If needed, swap over with someone else without pausing compressions.

Use an automated external defibrillator (AED) available in many public places:

  1. An AED provides a shock that may restart the heart.
  2. Follow the instructions on the defibrillator or listen to the guided instructions.
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Blood clots form when structures in the blood come together, creating solid clumps. This can happen due to endothelium damage, a tendency for blood clotting, and decreased blood movement in a blood vessel.

Blood clots often develop in coronary arteries but can also originate within the heart due to conditions such as AFib.

There are many risk factors for blood clots. These include lifestyle-related factors, such as smoking and having overweight. People may also inherit a genetic predisposition for blood clots. Various health conditions, such as diabetes and atherosclerosis, can also increase the risk of blood clotting.

Coronary thrombosis may not cause symptoms at first but can eventually cause a heart attack. Symptoms include shortness of breath, fainting, and chest pain. These symptoms require immediate medical attention.