Myoglobin is a protein that binds oxygen and iron. Myoglobin originates in myocytes and  is released into circulation with any damage to muscle tissue, including myocardial necrosis. Since skeletal muscle contains myoglobin, this measurement in quite non-specific for myocardial infarctions. The benefit lays in the fact that a detectable increase is seen only 30 minutes after injury occurs, unlike troponin and creatine kinase which can take 3-4 hours.