Myosin essential light chain (ELC), ventricular/cardiac isoform is a protein that in humans is encoded by the MYL3 gene. This cardiac ventricular/slow skeletal ELC isoform is distinct from that expressed in fast skeletal muscle (MYL1) and cardiac atrial muscle (MYL4). Ventricular ELC is part of the myosin molecule and is important in modulating cardiac muscle contraction. Mutations in MYL3 have been identified as a cause of familial hypertrophic cardiomyopathy, and associated with a mid-left ventricular chamber type hypertrophy. Five mutations in MYL3 have been identified to date: M149V, R154H, E56G, A57G and E143K. All of these cluster around two of the four EF-hand domains, suggesting that proper conformation in these regions is necessary for normal cardiac function.