The concept of use, or rate, dependency relates to the fact that drugs which bind to the sodium channel do so when the channel is in its open state and unbind, or dissociate, from the channel when it is closed. The speed (or kinetics) of this interaction determines how much of the drug (shown in red) is bound to the sodium channel at the end of each cardiac cycle. If the kinetics of dissociation are rapid, as illustrated here, almost all of the drug will leave the channel during diastole.