Myosin heavy chain 11(MYH11) is a smooth muscle myosin belonging to the myosin heavy chain family. It is a subunit of a hexameric protein that consists of two heavy chain subunits and two pairs of non-identical light chain subunits. Myosin heavy chain functions as a major contractile protein converting chemical energy into mechanical energy through the hydrolysis of ATP. An aberration in this protein is associated with acute myeloid leukemia of the M4Eo subtype.MYH labels smooth muscle cells and myoepithelial cells in various tissues. The immunoreactivity in glial cells of the cerebellum and spermatocytes in the testis is also observed. MYH has been a useful marker for myoepithelial cell as well as smooth muscle cell differentiation.