The selection of an effective and well-tolerated antiarrhythmic drug requires a systematic approach. Two methods for evaluating drug effect are routinely used--noninvasive techniques involving monitoring and exercise testing, and an invasive approach utilizing electrophysiologic testing. Each method has strengths and weaknesses and they must be applied to the appropriate patient. The evaluation of drug effect involves two types of testing. The acute drug test is a rapid screening of drug action, while a short-term maintenance period confirms drug efficacy and permits exposure of side effects. One of the most serious toxic effects is drug-induced aggravation of arrhythmia. An additional benefit of a systematized protocol is the identification of several effective agents that may be administered in combination to enhance antiarrhythmic drug effect. If an effective and well-tolerated drug is prescribed, recurrent malignant arrhythmia can be prevented.