Baroreflex sensitivity (BRS) has rapidly gained considerable attention as a result of multiple experimental and clinical reports on its prognostic value after a myocardial infarction. This article reviews the several aspects related to the use and significance of BRS. The methodology of baroreflex testing in man is described. The complex pathophysiology underlying BRS and the hypotheses proposed to explain its frequent reduction after a myocardial infarction are discussed. The section on experimental data also provides a rationale to understand the relation between increased vagal activity and reduced propensity for ventricular fibrillation. The article focuses largely on the clinical studies relating BRS and risk of cardiac mortality and also discusses the several attempts to modify this marker of reflex vagal activation.