CK-MB is an isoenzyme of creatine kinase. Creatine kinase dephosphorylates creatine phosphate to creatine, providing the energy required for ATP regeneration.

In 1966 creatine kinase isoenzymes were identified in various tissues. The isoenzymes of CK are dimers of either type B or type M polypeptide chains, BB isoenzymes are found in the central nervous system, MM isoenzyme is a principal component in adult skeletal muscles. The myocardium has 15% CK-MB isoenzyme and 85% CK-MM. Skeletal muscles contain about 1% to 3% of CK-MB.