A mural thrombus is an organizing blood clot attached to the wall of a blood vessel or the endocardium of the heart. It is composed of platelets, fibrin, and trapped red and white blood cells. As mural thrombi organize, they form characteristic alternating layers of fibrin and trapped cells, called lines of Zahn. A mural thrombus may occlude local blood supply, causing ischemic injury, or detach from the wall and embolize to cause injury at a distant location. Thrombosis risk factors are commonly described using Virchow's triad: endothelial injury, hemostasis, and hypercoagulability.

Mural thrombi of the heart most commonly occur from atrial fibrillation, endocarditis, or post myocardial infarction. Mural thrombi can be treated by acute thrombolysis or by long-term anticoagulation, depending on the clinical scenario.