Source Naturals Malic Acid is a combination of malic acid and magnesium. It supports proper muscle function, cardiovascular health, and energy production. Malic acid is a natural fruit acid that is present in most cells in the body and is an intermediate in the Krebs cycle, where energy is captured during the metabolism of carbs and fats. Magnesium plays an important role in muscle relaxation and is an essential cofactor for over 300 enzymatic reactions in metabolism, ATP synthesis, and energy production.*