The authors used programmed ventricular stimulation in 38 patients who had during Holter monitoring severe ventricular arrhythmias (greater than or equal to Lown 4a). The group comprised patients with IHD (22x), hypertrophic (11x) and dilatating cardiomyopathy (2x). Three patients had no organic heart disease. Nine patients were treated at the time of examination with antiarrhythmic drugs. In a total of 16 patients it proved possible to provoke ventricular tachycardia (VT)--four times permanent ventricular tachycardia, 12x transient ventricular tachycardia (NSVT). In the group of treated patients SVT was provoked twice and NSVT also twice, always in patients who took amiodarone. Using programmed ventricular stimulation the following antiarrhythmic drugs were tested: mexiletine, cordarone, ajmaline. The capacity of all tested antiarrhythmics in the prevention of VT was comparable. A total of two patients died during the investigation, in both cases a sudden death. One suffered from hypertrophic cardiomyopathy, one from IHD. In both on Holter monitoring NSVT episodes were revealed. Programmed stimulation provoked in both SVT, both were treated at the time of death with tested antiarrhythmics. The authors conclude that programmed ventricular stimulation is a suitable method for rationalization of antiarrhythmic treatment, the clinical results, however, do not correspond to laboratory results. They recommend therefore to use also Holter monitoring of patients at risk.