Beta-adrenergic blockers provide significant cardioprotection during acute ischemia and reperfusion. To further explore the effects of additional alpha-1-adrenoceptor blockade on autonomic modulation in acute myocardial infarction (AMI), carvedilol was compared with metoprolol in the setting of primary percutaneous coronary interventions (PCI). In a prospective study, 100 consecutive patients (61.1 +/- 11 years; 23 females) undergoing primary PCI for AMI were randomly assigned to metoprolol 200 mg/day vs carvedilol 25 mg/day. The first oral dose of study drug was administered upon hospital admission, and a 24-hour ambulatory electrocardiogram was recorded. A total of 40 recordings of patients assigned to metoprolol and 39 of patients assigned to carvedilol were eligible for analysis of heart rate turbulence. Turbulence onset (TO), turbulence slope (TS), and turbulence timing were measured after ventricular premature beats (VPBs). The mean value of the 10 preceding RR intervals (mean RR) before VPBs was also measured. There were no significant differences in mean age, gender distributions, TIMI perfusion grades, left ventricular ejection fraction, site and size of infarction, duration of ischemia, and mean 24-hour heart rate between the two groups. Though the mean RR were not significantly different (metoprolol 863.1 +/- 157 ms; carvedilol 839.6 +/- 151 ms), there was a trend toward lower values of TO in the carvedilol group (-0.015 +/- 0.016 vs -0.012 +/- 0.023%; P = NS) and significantly higher values for TS in the metoprolol group (6.96 +/- 5.8 vs 5.6 +/- 4.22; P < 0.05). Turbulence timing was similar in both groups (metoprolol 5.8 +/- 2.4 vs carvedilol 6.1 +/- 2.1). In patients undergoing direct PCI for AMI, treatment with carvedilol, in contrast to metoprolol, was associated with a higher early acceleration and a lower deceleration of heart rate after VPBs, indicating differing effects on baroreceptor response due to additional alpha-1-adrenoceptor blockade. These data offer new insights into effects of a broader antiadrenergic therapy on autonomic reflexes in the acute phase of AMI.