Coenzyme Q10 (also known as Q10) is a vitamin-like substance with a central role in cellular energy metabolism. The compound contributes actively in the conversion of fat, carbohydrate, protein, and alcohol to ATP (adenosine triphosphate), a molecule that stores energy in its chemical form. When a cell needs energy it breaks down the ATP molecule and releases the energy trapped inside. The entire process takes place inside the cells in some small bean-shaped structures called mitochondria. Muscle cells are particularly dependent on large amounts of energy which is why muscle cells contain substantially more mitochondria than other types of cells. The heart muscle is a good example of body tissue with cells that contain a large number of mitochondria and have a correspondingly large energy requirement.