Creatine kinase (CK), also known as creatine phosphokinase (CPK) or phosphocreatine kinase, is an enzyme (EC 2.7. 3.2) expressed by various tissues and cell types. When muscle tissue is damaged, CPK leaks into your blood. Therefore, high levels of CPK usually indicate some sort of stress or injury to your heart or other muscles. To test CPK, blood is drawn from a vein in your arm. In the hospital, a person's CK-MB level is often checked when they exhibit signs of heart attack. When the total CPK level is very high, it most often means there has been injury or stress to muscle tissue, the heart, or the brain. Muscle tissue injury is most likely. Finding which specific form of CPK is high helps determine which tissue has been damaged.