We have recently characterised, using time-resolved USAXS and SAXS data at ID021, the kinetics of the structural changes in the cardiac thick filament during the unitary mechanical response elicited by electrical stimulation of an intact cardiac trabecula at constant length. In particular we determined the structure, dynamics and function of the myosin motor domains in different regions of the thick filament during contraction. Now we propose to investigate the effect of myosin-targeting drugs on the dynamics of the regulatory structural changes of the myosin filament that control the rates of contraction and relaxation in electrically paced isolated intact cardiac trabeculae.