Myoglobin is a protein that is present in your heart and skeletal muscles. It captures the oxygen required for your muscles to function. Occurrence of a heart attack or severe muscle damages leads to the release of myoglobin into the blood stream. The levels of myoglobin increase after 2 to 3 hours after muscle and it peaks about 8 to 12 hours later. This test is administered in the case of a severe muscle injury or cases in which a heart attack is suspected. Symptoms which warrant a myoglobin test include muscle pain, dark coloured urine (too much of myoglobin might lead to a kidney failure), unexplained fever and fatigue, nausea and vomiting, and abdominal pain.