Three isoenzymes of creatine kinase (CK) are available: CK-BB, CK-MM, and CK-MB. The myocardium is the principal source of CK-MB, and it is also found in the skeletal muscle. When there is a myocardial damage, the CK-MB levels increase. In an extreme condition, the elevated levels can be due to skeletal muscle cell turnover, crush injuries, hypothyroidism, pulmonary embolism, muscular dystrophy, rhabdomyolysis or carbon monoxide poisoning. Today, CK-MB test is replaced by troponin assays; however, it is used in the case of abnormal troponin level or in the case of a suspected heart attack.