Magnesium plays an essential role in over 300 enzyme reactions in the human body. All refined foods are lacking magnesium, as well as most other essential minerals. Most Americans eat a highly refined diet and are, as a result, deficient in magnesium.
Magnesium regulates calcium transport and deposition into bone. It is necessary for tissue growth and development, immune system health and function, and the maintenance of normal intracellular calcium, potassium, and sodium levels.
One of magnesium's critical roles is in the conduction of nerve impulses and the relaxation of muscle tissue. Calcium and potassium stimulate muscle contraction -- magnesium makes muscles relax. This is very critical for heart function as you need ample stores of magnesium to allow for proper heart muscle relaxation. A lack of tissue magnesium has been implicated in cardiac failure.