Myosin is a highly conserved, ubiquitously expressed protein that hydrolyzes ATP, and this reaction provides the energy required for muscle contraction that interacts with actin to generate the force for cellular movements. It is a hexameric protein composed of four light chains and two heavy chains, each containing an actin-binding site and an ATP hydrolysis site. The heavy chains are encoded by the MYH gene family and were first isolated from a human fetal skeletal muscle and are the major determinant in the speed of contraction of skeletal muscle. Cardiac myosin exists as two isoforms in humans, Alpha-cardiac myosins and beta-cardiac myosins. These two isoforms are expressed in different amounts in the human heart. Beta-cardiac myosin s the predominant form during normal physiology while the alpha-isoform contributes for approximately 7% of the total myosin. Mutations of the MYH genes are associated with several different dilated and hypertrophic cardiomyopathies.