This tracing is from a 75 year old male who attempted suicide by ingesting amitriptyline, a tricyclic antidepressant that binds to the sodium channel in a use- or rate-dependent fashion causing a rate dependent decrease in the maximum rate of rise (dV/dt max) of the action potential upstroke, slowing of inter and intra-ventricular conduction, and an increase in the duration of the QRS complex. These effects become more pronounced at more rapid rates. The marked prolongation of the QRS complex shown here (it measures more than 0.20 seconds) is a manifestation of this use dependent sodium channel block.