Malignant hyperthermia is a peculiar disorder of muscle metabolism which is known to occur in man, swine, and many other mammalian species. It can occur as a a complication to the administration of anesthesia.
The metabolic process in muscle tissue that burns such chemicals as carbohydrates or fats, producing energy in the form of energetic molecules like ATP, so that the muscle fibers then have the energy available to contract and do work, is called oxidative phosphorylation.
The net result is to turn stored chemical energy in the form, typically, of carbohydrate, into carbon dioxide, water, heat, and muscular activity. This is why vigorous activity makes your body warm up, makes you sweat, makes you pant. It is also why shivering works to warm up a cold body.
What happens in malignant hyperthermia is termed an "uncoupling" of oxidative phosphorylation. The metabolic energy plant is turned on to its maximum setting, but largely (but not completely) divorced from the normal "connection" to muscular motor activity. Thus heating occurs in the absence of muscular contraction. In a full-blown case, this occurs throughout the body, in all skeletal muscles.
The results are a rapid increase in heart rate, an EXTREME increase in carbon dioxide production, a severe acidosis (increased acidity of the blood and tissues), and increased heat production and therefore body temperature. It must be emphasized that this severe, full-blown form, in people, in the best medical centers, still has a mortality -- that is a death_-rate -- of 30-50%.
While there are many things that must be done in the patient in the operating room to decrease the risk to life -- , discontinuing any triggering anesthetic agent, hyperventilating the lungs, cooling the body with ice packs and cold saline solution washed into the stomach and any open body cavities -- there is only one medication that has been shown to be truly useful as of the date of this essay and I know about its use in humans - that agent is dantrolene sodium, which must be given intravenously in large quantities.