Two patients with ischemic heart disease had sudden death detected by means of ambulatory electrocardiography; the first patient had ventricular tachycardia-asystole and the second bradycardia-asystole without mediating a ventricular tachyarrhythmia. In both cases the autonomic function of the heart was determined, by means of the heart rate variability for spectral analysis and for time domain analysis. An important decrease in heart rate variability in the patient with tachyarrhythmia was appreciated, more pronounced in the hour previous to his death. On the other hand, in the patient with bradycardia-asystole there was increased heart rate variability. This suggests different neural influences in both patients for the development of sudden death: an alteration in the autonomic function of the heart in the patient with ventricular tachyarrhythmias, related to a depressed parasympathetic tone. In the patient with bradycardia-asystole, the parasympathetic tone was accentuated.