Creatine Kinase MB (CK-MB) is an enzyme found primarily in the heart muscle. The CK-MB test measures the level of this enzyme in the blood and is used to diagnose heart-related conditions, particularly myocardial infarction (heart attack). When the heart muscle is damaged, such as in a heart attack, CK-MB is released into the bloodstream. Elevated levels of CK-MB indicate recent heart muscle injury. The test can help differentiate between heart-related damage and other muscle injuries, as CK-MB is more specific to cardiac muscle than other types of creatine kinase (CK).