Drugs may induce changes in the electrocardiogram by one or more of several mechanisms. These include the following: --By directly binding with ion channels thereby affecting ionic conductance. --By interacting with autonomic receptors and by this mechanism altering ionic currents. --By influencing the sodium/potassium pump thereby affecting intracellular sodium and potassium, and by this mechanism influencing ionic currents. --By affecting the compartmentalization of intracellular calcium. --By affecting extracellular ions-particularly potassium, thereby influencing ionic currents.