What is a blood clot formed within the heart or a blood vessel during life called?

A blood clot that forms within the heart or a blood vessel during life is referred to as a thrombus. This term specifically indicates that the clot has developed in situ—meaning it has formed at the site where it is found, rather than being carried there by the bloodstream. Thrombi can lead to various complications depending on their location, such as obstruction of blood flow, which can result in tissue damage or other serious health issues.

In contrast, an embolus is a term for a clot or other substance that travels through the bloodstream and can cause a blockage in a different area from where it originated. Hemorrhage refers to the escape of blood from a ruptured blood vessel, which is unrelated to the formation of a blood clot. Ischemia is a condition characterized by insufficient blood flow to a part of the body, often due to an obstruction, but it does not specifically denote the presence of a clot. Thus, knowing the definitions and distinctions between these terms clarifies why a thrombus is the correct answer in this context.