It has been verified that losartan has beneficial effects on ventricular remodeling (VRM) after acute myocardial infarction (AMI), but the effects of carvedilol alone or in combination with losartan on this condition have not been defined. The present study used rats to compare the effects of carvedilol and losartan alone and in combination for preventing VRM after AMI. After ligation of the left coronary artery, 100 surviving female Sprague-Dawley rats were randomly assigned to 1 of 4 groups: (1) AMI control (n=25), (2) carvedilol (Car, 1 mg x kg(-1) x day(-1)) (n=25), (3) losartan (Los, 3 mg x kg(-1) x day (-1)) (n=25), and (4) Car (1 mg x kg (-1). day(-1)) + Los (3 mg x kg(-1) x day (-1)) (n=25). A sham-operated group (n=17) was also randomly selected. Drugs were administered by gastric gavage for 4 weeks. After hemodynamic studies, the hearts were fixed and analyzed pathologically. Exclusive of the rats that had died or had an infarct size <35% or >55%, complete data were obtained for 65 rats, comprising AMI control (n=13), Car (n=12), Los (n=13), combination (n=14), and sham (n=13) groups. There were no significant differences in the size of infarct among the 4 AMI groups (45.8 approximately 46.7%, all p>0.05). Compared with the sham group, left ventricular (LV) end-diastolic pressure (LVEDP), volume (LVV), weight (LVW) and septal thickness (STh) were all significantly increased (all p<0.001), whereas +/-dp/dt was significantly decreased (both p<0.001) in the AMI group. In comparison with the AMI group, LVEDP, LVV, LVW and STh were all significantly decreased (LVEDP: 12.7+/-2.3, 9.7+/-2.8, and 8.6+/-3.5 mmHg vs 20.6+/-2.7 mmHg, all p<0.001; LVV: 0.74+/-0.07, 0.76+/-0.07, and 0.70+/-0.09 ml vs 0.86+/-0.05 ml, all p<0.05; LVW: 668.4+/-52.0, 702.6+/-45.4, and 683.9+/-67.7 mg vs 787.3+/-76.7 mg, p<0.05 approximately 0.001; STh: 1.57+/-0.05, 1.48+/-0.07, and 1.46+/-0.07 mm vs 1.71+/-0.04 mm, all p<0.05), whereas +/-dp/dt was significantly increased (all p<0.05) in the Car, Los, and combination groups, with LVEDP decreasing more in both Los and the combination groups than in the Car group alone (p<0.05) and STh decreasing more in the combination group than in the Car group alone (p<0.05). Carvedilol and losartan alone and in combination all prevent VRM after AMI in rats, with almost equivalent effect.