Myoglobin (MYO or MB for short) is a small molecule pigment protein, which is composed of globin and heme. It can reversibly bind with oxygen to form MbO2, which is called oxygenated myoglobin, and MB is called deoxymyoglobin. It can transport and store oxygen in muscle cells. When the myocardium is damaged, it diffuses out of the cardiomyocytes and enters the blood circulation. Myoglobin only exists in cardiac muscle and skeletal muscle, and other tissues, including smooth muscle, do not contain this protein.