Deep Vein Thrombosis
Heart Health

Deep Vein Thrombosis: What to Watch For

Blood clots can be lifesavers. But a clot that forms deep in the body is dangerous. This kind of clot, known as a venous thromboembolism, or VTE, can cause pain, swelling, and redness in an affected limb, and can even be deadly, according to the January 2016 Harvard Heart Letter.

When a clot forms in a leg or arm, the Harvard experts say, it’s called deep-vein thrombosis. If the clot breaks off and travels to the lungs, it causes a pulmonary embolism. One or both of these conditions strike at least 900,000 Americans each year, killing at least 100,000. However, many people are unaware of the symptoms or the gravity of VTE. Pulmonary embolisms are twice as deadly as heart attacks.

Until recently, the Heart Letter says, doctors thought of VTE as a short-lived condition that could be successfully treated with a brief course of anti-clotting drugs. “We now understand that it’s a chronic illness — similar to diabetes and heart disease — that may require lifelong management,” says Dr. Samuel Z. Goldhaber, senior cardiologist at Harvard-affiliated Brigham and Women’s Hospital.

The same factors that make people more likely to have heart disease, such as high blood pressure, smoking, and obesity, also make them more susceptible to a VTE. Most occur in people ages 60 and older, but younger people can get them, too. Here, the Harvard experts say, are symptoms:

Symptoms of deep-vein thrombosis

The affected area may be

*Tender or painful, with no known cause and worsening over time

*Swollen, red, and warm to the touch.

If these symptoms linger for more than a few hours, the Harvard experts say, call your doctor for advice.

Symptoms of a pulmonary embolism

*Difficulty breathing that happens suddenly, without an explanation

*A fast or irregular heartbeat

*Chest pain or discomfort, which usually worsens with a deep breath or coughing

*Coughing up blood

*Very low blood pressure

*Feeling lightheaded or faint.

If you have these symptoms—especially if they worsen quickly over a period of hours—call 911 right away.

The Harvard experts also emphasize that damage to a blood vessel, from either an injury or surgery, can provoke a blood clot. Being confined to bed during a recovery period leads to sluggish blood flow, further increasing the risk. More than half of VTEs are related to a recent hospital stay or surgery. Undergoing treatment for cancer and prolonged sitting during long-distance travel also increases a person’s risk.  Between 5% and 8% of people have one of several inherited disorders that make them more prone to clots.

Anyone who is slated for surgery or confined to bed because of an illness or injury should ask his or her doctor about ways to prevent these blood clots from forming. For most people, walking as soon as possible after an operation can lower the risk. Doctors sometimes prescribe anti-clotting drugs for high-risk people after surgery. Another option is graduated compression stockings. These knee-high socks apply pressure to the lower legs, with the greatest pressure at the ankle. They gently increase blood flow from the ankle toward the thigh.

The Harvard Heart Letter is available from Harvard Health Publications, the publishing division of Harvard Medical School, for $20 per year. Subscribe at or by calling 877-649-9457 (toll-free).