There are at least two major functions of L-carnitine. All tissues except the brain use long-chain fatty acids for bioenergy production. In cardiac and skeletal muscle, a major contribution of bioenergy comes from the beta-oxidation of long-chain fatty acids.
Long-chain fatty acids require L-carnitine to transport them across the inner membranes of the mitochondria, wherein their metabolism produces bioenergy. Following the delivery of long-chain fatty acids into other mitochondria, L-carnitine, either by itself or esterified to an acyl group, recrosses the mitochondrial membrane to allow for continual use in this shuttle process.