A deep vein thrombosis (DVT) is a blood clot in a vein inside a muscle. Usually it's in a lower leg, thigh, pelvis, or arm.
"Typically, a person calls saying, 'I've had 3 or 4 days of swelling in one of my legs, and it won't go down,'" says Terri Remy, MD, of Primary Care Alexandria in Virginia.
Symptoms usually include swelling and sometimes pain and tenderness. But you won't always have them.