It's called deep vein thrombosis, or DVT. All our veins have small valves powered by the muscles around them. They keep blood moving toward the heart, instead of flowing backward inside veins.

When a blood clot forms in a vein deep inside your body, it causes what doctors call deep vein thrombosis (DVT).

Deep vein thrombosis (DVT) is a blood clot (thrombus) in a deep vein, usually in the legs. These clots require medical care right away. These clots are dangerous because they can break loose, travel ...