MH-susceptible persons have a mutation that results in the presence of abnormal proteins in the muscle cells of their body. Although normal in everyday life, when these patients are exposed to certain anesthetic agents, or in rare cases when exposed to high environmental heat or strenuous exercise, it causes an abnormal release of calcium from the sarcoplasmic reticulum (a storage site for calcium) in the muscle cell, which results in a sustained muscle contraction and thus an abnormal increase in metabolism and heat production. The muscle cells eventually are depleted of adenosine triphosphate (ATP) the source of cellular energy, and die, releasing large amounts of potassium into the bloodstream, causing hyperkalemia, followed by ventricular (cardiac) arrhythmias. The muscle pigment myoglobin is also released from the muscle cells and may be toxic to the kidney. Left untreated, these changes can cause cardiac arrest, kidney failure, blood coagulation problems, internal hemorrhage, brain injury, liver failure, and may be fatal. A more detailed explanation of the biochemical changes in MH may be found on the MHAUS website.