Autonomic nervous system dysfunction and low left ventricular ejection fraction have been associated with an increased incidence of cardiac arrhythmias and sudden death. This research was conducted to determine whether Valsalva ratio (longest to shortest R-R interval during Valsalva manoeuvre), R-R variability (standard deviation of R-R intervals in a 60-second electrocardiographic recording strip), and corrected QT interval permit the identification of those patients with an inducible sustained ventricular arrhythmia when submitted to electrophysiological studies. We also evaluated the ejection fraction as a predictive index of inducibility. We studied 42 patients (21 males), 38 ± 19 years old, who were submitted to an electrophysiological study in order to evaluate supraventricular (control group: n = 16) or ventricular arrhythmias (n = 26). The patients studied for the evaluation of ventricular arthythmias presented structural and functional cardiac damage. Their ejection fraction (0.41 ± 0.17) was significantly reduced (p = 0.01) when compared to that of the control group (0.61 ± 0.08). The patients with cardiac damage had abnormal autonomic nervous system test results. None of the measurements was significantly related to the inducibility of sustained ventricular tachyarrhythmias in the group of patients who had structural and functional involvement. The finding of abnormal cardiac autonomic nervous system indices and low ejection fraction can be related to structural heart disease, but neither the abnormal cardiac autonomic nervous system indices nor the low ejection fraction allows us to identify the patients who will develop inducible sustained ventricular tachyarrhythmias when submitted to electrophysiological study.