The authors evaluated the incidence of late ventricular potentials (LVP) in 84 patients (63 men and 21 women) with programmed stimulation of the ventricles. At the same time they described the relationship of the mentioned potentials to the finding of ventricular ectopic arrhythmias during ECG monitoring and left ventricular function (ultrasonographic examination). Non-invasive recording of late ventricular potentials is due to the assessed sensitivity, i.e. 73%, and specificity i.e. 67% (in relation to the results of programmed ventricular stimulation) a useful method for evaluation of the arrhythmogenic substrate of the heart muscle. The authors detected LVP in 35% of 37 subjects without arrhythmias, in 58% of 31 subjects with premature ventricular contractions class 3 to 5 according to Lown and in 60% of 15 subjects with relapsing ventricular tachycardias. LVP are more frequent in patients with impaired left ventricular function. They were recorded during the ejection fraction of the left ventricle beneath 50% in 69% of 16 subjects and in the left ventricular ejection fraction above 50% in 44% of 68 subjects.