A blood clot that forms on and remains attached to the inside wall of a blood vessel or the heart.

A thrombus is a mass of clumped blood, called a blood clot, that forms on and remains attached to the inside wall of a blood vessel.

A thrombus often obstructs blood flow. This can deprive tissues of the blood and oxygen they need. Over time, this may lead to damage or death of the tissues.

Symptoms depend on the location of the clot. Blood clots that stick to the wall of a vein in an arm or leg can cause pain, redness and swelling.

Treatment for blood clots typically includes taking blood-thinning medicines. Rarely, the clot may need to be removed by a catheter.