This study examined the relation between heart rate variability (HRV) and baroreflex sensitivity (BRS) and subsequent major arrhythmic events (MAE), defined as sustained VT, VF or sudden death, in 263 patients with idiopathic dilated cardiomyopathy (IDC) in sinus rhythm. The predefined measure of HRV was the standard deviation of all normal-to-normal RR intervals (SDNN) on baseline 24-hour ambulatory ECG. BRS was determined by the phenylephrine method. Over 52 +/- 21 months of follow-up, MAE occurred in 38 patients (14%). SDNN at baseline 24-hour ambulatory ECG (106 +/- 46 vs 109 +/- 45, ns) and BRS (7.9 +/- 5.5 vs 7.7 +/- 5.3 ms/mmHg, ns) were both similar in patients with versus without MAE during follow-up. In contrast, left ventricular ejection fraction was significantly lower in patients with versus without MAE (24%+/- 7% vs 31%+/- 10%, P < 0.019. CONCLUSIONS: Neither HRV nor BRS predicted MAE in patients with IDC.