Contractile protein that plays a role in heart development and function (PubMed:10409661). Following phosphorylation, plays a role in cross-bridge cycling kinetics and cardiac muscle contraction by increasing myosin lever arm stiffness and promoting myosin head diffusion; as a consequence of the increase in maximum contraction force and calcium sensitivity of contraction force. These events altogether slow down myosin kinetics and prolong duty cycle resulting in accumulated myosins being cooperatively recruited to actin binding sites to sustain thin filament activation as a means to fine-tune myofilament calcium sensitivity to force (By similarity) (PubMed:22426213, PubMed:16908724, PubMed:10409661). During cardiogenesis plays an early role in cardiac contractility by promoting cardiac myofibril assembly (PubMed:9422794). Myosin is a hexamer of 2 heavy chains and 4 light chains (By similarity). Interacts with MYOC (By similarity). Abundantly expressed in both cardiac and slow skeletal muscle (PubMed:1379240). In the adult heart, the phosphorylated form is highly expressed in epicardium and weakly in endocardium (PubMed:22426213). At 8 dpc highly expressed in the ventricular portion of the heart tube, with no detectable expression in the atrial or sinus venosus regions; also expressed in the proximal outflow tract of the heart tube at minimally detectable levels. At 9-10 dpc expression is well established in the proximal outflow tract region adjacent to the ventricular segment. At 11 dpc, expression becomes restricted to the ventricular region. N-terminus is methylated by METTL11A/NTM1. Phosphorylated by MYLK3 and MYLK2; promotes cardiac muscle contraction and function. Dephosphorylated by PPP1CB complexed to PPP1R12B (By similarity). The phosphorylated form in adult is expressed as gradients across the heart from endocardium (low phosphorylation) to epicardium (high phosphorylation); regulates cardiac torsion and workload distribution (PubMed:22426213). Myl2 homozygous die at 12.5 dpc, which is associated with ultrastructural defects in ventricular sarcomere assembly, that included disruptions and disorganization of the normal parallel alignment of the thick and thin filaments, narrower fiber widths and larger distances between Z disks and misalignment of Z-band between sarcomeres. This chain binds calcium.