Contraction in cardiac muscle occurs due to the the binding of the myosin head to adenosine triphosphate ( ATP ), which then pulls the actin filaments to the center of the sarcomere, the mechanical force of contraction.

How do cardiomyocytes contract simultaneously?

When two independently beating embryonic cardiac muscle cells are placed together, the cell with the higher inherent rate sets the pace, and the impulse spreads from the faster to the slower cell to trigger a contraction. As more cells are joined together, the fastest cell continues to assume control of the rate.

How do myocytes contract?

Chemical and physical interactions between the actin and myosin cause the sarcomere length to shorten, and therefore the myocyte to contract during the process of excitation-contraction coupling. The interactions between actin and myosin serve as the basis for the sliding filament theory of muscle contraction.