VT may be observed to accompany a wide variety of heart diseases and occasionally no heart disease at all. The efficacy of drug therapy is dependent on antiarrhythmic effects and the mechanism underlying the patient's VT. Conventional antiarrhythmic agents appear to be effective in no more than one third of patients, but a substantial number of other potentially useful antiarrhythmic agents exist. Unfortunately, their effectiveness in treating sustained VT for the most part must still be proved. Other agents such as amiodarone appear effective, but ways to predict which patients will benefit remain unknown. Invasive and noninvasive techniques exist for assessing therapeutic efficacy, but determination of which is more appropriate awaits a wider experience and more direct comparison.