The existence of ventricular tachycardia in subjects without detectable heart disease has been recognized for more than half a century. These rhythms occur in younger individuals and account for about 5% of referrals to the electrophysiology service. In contrast, ventricular tachycardia in the setting of chronic ischemic heart disease occurs in an older age group and accounts for more than 90% of all referals. It is important to be able to distinguish between the different varieties of ventricular tachycardia, because in patients without structural heart disease sudden cardiac death is rare, compared with the very high mortality associated with postischemic recurrent ventricular tachycardia. The natural history of ventricular tachycardia occurring without structural heart disease tends to be benign even when the tachycardia is untreated. Thus these rhythms are more of an annoyance than a life-threatening event. This variety of ventricular tachycardia is frequently not inducible by atrial or ventricular programmed stimulation but is inducible by atrial or ventricular pacing, exercise testing, or isoproterenol infusion. The ventricular tachycardia in patients without structural heart disease is frequently responsive to drugs such as β-blockers, verapamil, or adenosine that have little or no effect on ventricular tachycardia associated with previous infarction. These differences strongly suggest the possibility of a tachycardia mechanism other than reentry, although conclusive evidence is still lacking. © 1993.