There are two other important features which impact on the electrophysiologic effects of the type I and type III anti-arrhythmic drugs and the effects of these drugs on the electrocardiogram. These are: The concept of USE (or rate) DEPENDENCY which applies primarily to drugs that bind to the sodium channel, i.e, the class I drugs and amiodarone The ability of the drugs to cause serious and often life-threatening ventricular arrhythmias, a PRO-ARRHYTHMIC EFFECT, which applies primarily to drugs that bind to potasssium channels, i.e, the class III and class Ia drugs.