Myoglobin

Myoglobin is a protein in muscle tissue that holds oxygen and iron. It is chemically similar to hemoglobin. It is found in most mammals. It is held in particularly high concentrations in animals that spend a great deal of time underwater as it can assist with the storage of oxygen within the body's tissues. 
Myoglobin is only released when muscle tissue is damaged. Small amounts are routinely filtered by the kidneys, so in a normal patient, myoglobin should not be detectable in the bloodstream. 
High myoglobin levels are typical of rhabdomyolysis. Moreover, although myoglobin is not toxic, in an acidic environment it is converted to ferrihemate, which can cause kidney failure. 
If a heart attack is suspected, the presence of myoglobin can indicate damage to the heart.
Myoglobin at Wikipedia
Category:Physiology