Background:Depressed heart rate variability (HRV) is associated with increased risk for sudden cardiac death after myocardial infarction. Beta‐blocker therapy reduces the risk of sudden cardiac death in patients with recent infarction. There is also evidence that beta‐blockers improve HRV in postinfarction patients. In this study, we investigated whether the association between HRV and cardiac mortality in postinfarction patients is different in those who, on clinical grounds are and are not discharged on beta‐blocker therapy.Methods:HRV was assessed from 24‐hour ambulatory electrocardiograms before hospital discharge in 438 survivors of acute myocardial infarction. After the recordings, 147 patients were prescribed beta‐blockers and 291 were discharged without beta‐blocker therapy. The patients were followed for at least 2 years using cardiac death and arrhythmic death as clinical endpoints. Patients were dichotomized to depressed and normal HRV at the lowest 30 percentile.Results:Multivariate logistic regression analysis showed that HRV was a sigificant determinant of cardiac (P<0.001) and arrhythmic mortality (P<0.001) in patients who were not on beta‐blocker therapy, whereas it was not a predictor of cardiac or arrhythmic mortality in patients who were taking beta‐blockers. Beta‐blocker therapy was associated with a significantly lower total cardiac mortality and arrhythmic mortality in patients with depressed HRV (P<0.01 and P<0.05, respectively). In patients with normal HRV, the reduction of mortality was smaller and remained nonsignificant.Conclusion:HRV was not a predictor of cardiac mortality in postinfarction patients who were prescribed beta‐blockers before hospital discharge. In addition, beta‐blocker therapy was associated with a lower cardiac mortality, particularly in patients with depressed HRV. Thus, depressed HRV might be considered as an additional indication for beta‐blocker therapy in