Background Although angiotensin-converting enzyme inhibitor attenuates ventricular enlargement, whether β-blocker therapy induces regression of left ventricular remodeling is not known. The purpose of this study was to compare the effects of bisoprolol therapy with those of imidapril therapy on left ventricular remodeling after acute myocardial infarction (AMI). Methods Sixty patients with AMI who underwent reperfusion therapy were randomly assigned to an imidapril group (20 patients), a bisoprolol group (20 patients), or a control group (20 patients). Administration was started within 24 hours. Left ventricular function on admission and 3 months and 1 year after AMI was investigated. Results Baseline characteristics on admission were similar in the 3 groups except for sex distribution. Mean pulmonary capillary wedge pressure and left ventricular end-diastolic pressure in the bisoprolol group were higher than those in the imidapril group 1 year after admission (pulmonary capillary wedge pressure: 12 ± 7 vs 8 ± 2 mm Hg, left ventricular end-diastolic pressure: 17 ± 8 vs 11 ± 4 mm Hg, P <.01). Left ventricular end-diastolic volume index (EDVI) increased in the bisoprolol group throughout the 1-year period (P <.01), whereas EDVI in the imidapril group decreased (P <.01). The increases in EDVI during 1 year in the bisoprolol group were greater than those of the other 2 groups (bisoprolol: 12 ± 10, imidapril: –9 ± 7, control: 4 ± 11 mL/m², P <.01). Conclusions Early treatment with bisoprolol in AMI cannot prevent left ventricular remodeling, whereas imidapril attenuates left ventricular dilation by decreasing preload. (Am Heart J 2000;140:e27.)