Blood returns to the heart through veins. When the blood clumps together and turns into solid material, it is called a blood clot. When the clot is in the deep vein it is called deep vein thrombosis (DVT), which usually occur in the leg veins. This condition can quickly lead to pulmonary embolism (PE), a blood clot in the lung, which is life threatening. https://advancedheartandvein.com/conditions/deep-vein-thrombosis/