Sometimes people develop a blood clot after surgery or after sitting still for a long period of time such as on a multi-hour plane ride. The condition is called deep vein thrombosis.
It happens when a blood clot—the medical term is "thrombus"—develops in a deep vein of the body. It occurs most commonly in the legs.
If the blood clot travels to the heart and lungs, it can cause pulmonary embolism—the sudden blocking of an artery to the lung. Combined deep vein thrombosis and pulmonary embolisms are referred to as venous thromboembolisms, which is diagnosed in about two million Americans each year, claiming more than 100,000 lives annually.