Carnitine is made in the body from the amino acids lysine and methionine. Carnitine is often called an amino acid because of its chemical makeup, however it is actually a vitamin-like nutrient, related in structure to the B vitamins. It plays an essential role in transporting fatty acids into the muscles for energy, and is needed to transport these substances into the heart muscle. Nearly 60% of the energy for the heart muscle is supplied by fatty acids. It is also one of the two amino acids which promote sperm motility.