BACKGROUND: It is well-known that a reduction of the cardiac frequency variability, measurable with the Heart Rate Variability (HRV) system, is an indirect expression of the sympathetic-autonomic tone. Another index, Heart Rate Turbulence (HRT), has been recently suggested as a possible unit of measurement for the sympathetic-autonomic tone: this system allows to estimate the baro-reflex response of the carotid arteries to an early ventricular extra-systole by analysing heart rate variations induced by a premature beat. METHODS AND RESULTS: In our research we have analyzed this phenomenon in patients affected by moderate or severe cardiac failure. In particular, we divided 110 patients into two arms: subjects with or without a history of resuscitated arrhythmic death, that is, patients with high or low arrhythmic potential. In a detailed analysis of the sympathetic-autonomic tone, using both the above-mentioned parameters, HRV showed an irrelevant statistical difference between the two arms; on the contrary, HRT showed a significant statistical difference. CONCLUSIONS: If our conclusions will be confirmed by next larger reports, HRT could become a reliable index for screening the arrhythmic potential of patients affected by cardiac failure, to select the ones who need a defibrillator implantation.