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Blood clots are the clumps that occur when the blood hardens from a liquid to a solid (coagulates). A blood clot that forms inside a blood vessel or within the heart and remains there is called a thrombus.

A thrombus that travels from the blood vessel or heart to another location in the body is called an embolus. The disorder is called an embolism. For example, an embolus that occurs in the lungs is called a pulmonary embolism.

Sometimes other materials can act like an embolus and block blood flow, including:

• Air
• Amniotic fluid
• A piece of atherosclerotic plaque
• Fat clumps
• Small pieces of tumor

See also:

• Angina
• Arterial embolism
• Atheroembolic renal disease
• Deep venous thrombosis
• Heart attack
• Pulmonary embolism
• Renal vein thrombosis
• Stroke
• Thrombophlebitis

Thrombi and emboli can firmly attach to a blood vessel. They can partially or completely block the flow of blood in that vessel.

A blockage in the blood vessel prevents normal blood flow and oxygen from reaching the tissues in that location. This is called ischemia. If ischemia is not treated promptly, it can result in tissue damage, or death of the tissues in that area.

Clot; Emboli; Thrombi

Updated by: Sean O. Stitham, MD, private practice in Internal Medicine, Seattle, Washington; and James R. Mason, MD, Oncologist, Director, Blood and Marrow Transplantation Program and Stem Cell Processing Lab, Scripps Clinic, Torrey Pines, California. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.