Background The aim of this study was to describe the effect of intravenous metoprolol on the intensity of chest pain before hospital admission in patients with suspected acute myocardial infarction AMI). Methods and Results Two hundred sixty-two patients with acute chest pain and suspected AMI were randomly assigned before hospital admission to either 5 mg morphine plus metoprolol 5 mg × 3 intravenously or 5 mg morphine plus intravenous placebo. Chest pain was evaluated on a 10-grade scale before and for 60 minutes after intravenous injection. One hundred thirty-four patients were randomly assigned to metoprolol and 128 to placebo. Among all patients randomized to metoprolol, the mean chest pain score was reduced by 3.0 ± 1.9 arbitrary units AU) from before to after intravenous injection compared with 2.6 ± 2.1 AU for placebo not significant). Among patients with an initially confirmed or strong suspicion of AMI, the corresponding figures were 3.1 ± 1.8 AU for metoprolol and 2.2 ± 1.6 AU for placebo P = .02). Among patients with only a vague or moderate suspicion of AMI, there was no difference. The treatment was well tolerated. Conclusions When all patients were included in the analyses, there was no significant difference with regard to reduction of chest pain in the patients randomly assigned to metoprolol compared with placebo. A retrospective subgroup analysis indicated a beneficial effect of metoprolol among patients with an initially strong suspicion of or confirmed AMI. Further investigations are warranted to confirm this finding. Am Heart J 1999;137:821-9.)