Programmed electrical stimulation was performed in 54 consecutive patients with hypertrophic cardiomyopathy. Three patients had a history of cardiac arrest due to ventricular tachyarrhythmias (group A), eight patients had a history of syncope of unknown origin (group B), and 43 patients were "asymptomatic", i.e. they had no documented or suspected symptomatic ventricular arrhythmias (group C). There were no differences among the groups with respect to electrocardiographic, echocardiographic or hemodynamic data. Ventricular arrhythmias were induced by atrial and right and left ventricular stimulation with a maximum of two extrastimuli in 18 patients. Induced arrhythmias were repetitive ventricular response in six patients, nonsustained ventricular tachycardia in four, sustained ventricular tachycardia in five, and ventricular fibrillation in three patients. Ventricular tachycardia was always rapid with a mean cycle length of 194 +/- 20 ms. In one group A patient, rapid ventricular tachycardia was induced during atrial stimulation. The type and incidence of induced ventricular arrhythmias did not differ among the three groups. It is concluded that programmed stimulation with a maximum of two ventricular extrastimuli cannot distinguish between patients with hypertrophic cardiomyopathy who had either cardiac arrest or syncope or were "asymptomatic".