The last two decades have provided clear evidence for the tight and casual relation existing between arrhythmic mortality and the autonomic nervous system, particularly with imbalances characterized by decreases in vagal and/or increases in sympathetic activity. A series of compelling experimental results has represented the driving force for the clinical evaluation of the potential prognostic value of baroreflex sensitivity (BRS), a measure that can provide information on the capability to augment vagal activity. This article reviews the methodology more commonly used to quantify the clinical evaluation of this parameter, and then focuses on the key clinical studies highlighting those performed in postmyocardial infarction patients. Among them the most informative is ATRAMI, a multicenter prospective study involving almost 1300 patients. The main conclusion is that both heart rate variability and BRS are strong and independent risk factors for post-infarction mortality, thus demonstrating the clinical usefulness of autonomic markers.