Recently there has been increased interest in the analysis of heart rate variability (HRV) and baroreflex sensitivity (BRS) for postinfarction risk stratification. HRV and BRS are decreased in patients following myocardial infarction and both a reduced HRV and a depressed BRS identify a subgroup at higher risk of cardiac mortality and arrhythmic events. In a large trial of post-myocardial infarction patients the relative risk of mortality was 5.3 times higher in the group with depressed HRV (standard deviation of normal RR intervals over 24 hour recordings < 50 ms) than in the group with preserved HRV. These findings were later confirmed by both time domain and power spectral analysis of HRV. The predictive value of depressed HRV was found to be independent of other established risk predictors including other Holter features and left ventricular ejection fraction. By testing reflex vagal activity, in a series of 78 patients recovering from a first myocardial infarction, the risk of death increased more than 15 times in the presence of a markedly depressed BRS (< or = 3 ms/mmHg). In a subsequent study BRS was found to be the most significant predictor of induction of sustained monomorphic ventricular tachycardia at programmed electrical stimulation. BRS seems to be more valuable than HRV in the prediction of arrhythmic events by providing a relative risk four times greater than HRV to accurately predict inducibility to ventricular tachycardia. Additional data have shown that BRS but not HRV did clearly separate postinfarction patients with aborted sudden death from similar patients without ventricular tachycardia or fibrillation.(ABSTRACT TRUNCATED AT 250 WORDS)