Blood clots that form in the deep veins of the legs (deep-vein thrombosis, or DVT) can cause leg symptoms. Worse, the clots can break loose and travel through the blood to the heart and then to the lungs, causing a pulmonary embolism (PE).

More people die from PE each year in the United States than from breast cancer. What causes DVT and PE, what are the symptoms, and how can you prevent them?