A large blood clot that forms inside one of the deep veins in the legs, thighs, or pelvis.
DVT is most commonly associated with long periods of inactivity, such as a long airplane ride or hospital stay. Those with conditions that predispose them to the formation of blood clots are also at greater risk.
One of the most dangerous complications of a DVT is a pulmonary embolism -- a piece of the blood clot travels to the lungs, causing oxygen levels in the blood to become dangerously low. The blood clot can also travel through an abnormal hole in the wall inside the heart to the brain and cause a stroke.