DVT is the formation of a blood clot (thrombus) within the deep veins. The most common site for their formation is the legs thought it could take place in any vein of the body.
Most patients are not aware of having this problem. DVT itself is not life-threatening but the leg clots may break and pass via the blood to the lungs where they may cause blockage of the vessels causing acute lung failure. This is a life-threatening condition. Should one become breathless with leg swelling one should go to the casualty to exclude pulmonary embolism?