L-carnitine is an amino acid derivative that is essential to human life. Its primary function is to transport fatty acids from the fluid of the cells into the mitochondria, where they are used to produce energy in the form of ATP. The heart and endothelium which line the arteries depend largely on fats for fuel as do skeletal muscles when shifting into endurance mode. About 60%-70% of the energy used by the heart comes from the breakdown of fatty acids.
L-carnitine is also used to remove toxic by-products formed during the energy-producing process.