This study was designed to examine the ventricular vulnerability of patients with vasospastic angina. Fourteen patients (mean age 57 +/- 9 years) with vasospastic angina underwent electrophysiologic testing during the asymptomatic phase (baseline) and after the relief of acetylcholine-induced spasm with isosorbide dinitrates. Twenty patients without structural heart disease served as a control group. By programmed ventricular stimulation, polymorphic ventricular tachycardia (VT) was induced at baseline in 6 of 14 patients, with 1 patient developing ventricular fibrillation and 7 of 14 patients developing repetitive ventricular responses. After isosorbide dinitrate, polymorphic VT was induced in only 1 patient who had ventricular fibrillation at baseline. Repetitive ventricular responses were induced in 3 of 5 patients who had VT at baseline and in 4 of the 7 patients with repetitive ventricular responses at baseline. There was a significant difference in the incidences and severity of induced ventricular arrhythmias between the 2 phases (p <0.01). Among 20 control subjects, repetitive ventricular responses were induced only in 6 patients, but no VT was induced. There was a significant difference in the incidence of induced ventricular arrhythmias and VT at baseline between the vasospastic angina and control groups (p <0.001 and <0.01, respectively). Thus, patients with vasospastic angina had increased ventricular vulnerability, even during the symptom-free period without ischemic events, which could predispose to the development of life-threatening arrhythmias aggravated by vasospastic attacks.