For proper heart and muscle function and protein synthesis. Magnesium Citrate is very well absorbed because it is highly soluble. Citric acid forms a strong bond with magnesium so that it easily crosses the intestinal membrane. Magnesium regulates the energy producing system of the body . . . forming ATP the body's ready to use fuel that is needed for all breakdown and building processes. Magnesium opposes calcium in several enzymatic pathways and helps prevent excess nerve and muscle 'excitability.' Magnesium relaxes arterial walls, and thus is of great benefit in the management of arterial pressure and heart muscle stability. Two capsules provide 500 mg (125% USRDA) of Magnesium (citrate/oxide). Also contains magnesium stearate.