OBJECTIVE This study compared the effects of captopril and enalapril on left ventricular geometry, function and mass and on scar collagen and topography during healing after anterior and inferior myocardial infarction in a canine model. BACKGROUND The beneficial effect of prolonged angiotensin-converting enzyme inhibitor therapy on remodeling during healing after myocardial infarction might be greater in anterior than inferior infarcts and more effective with captopril than enalapril therapy. METHODS The effects of 6 weeks of therapy with captopril (50 mg twice a day), enalapril (2.5 mg twice a day) or placebo on in vivo variables of left ventricular remodeling, function and mass (by echocardiography), hemodynamic function, postmortem topography (by planimetry) and collagen (hydroxyproline levels) were studied in 36 instrumented dogs randomized to receive therapy 48 h after left anterior descending or left circumflex coronary artery occlusion. RESULTS Compared with placebo therapy, both captopril and enalapril decreased infarct expansion and thinning, progressive ventricular dilation, ventricular mass and asynergy and infarct collagen levels in anterior and inferior infarcts. Despite similar small scar sizes, the effects on remodeling and dysfunction were greater in anterior than inferior infarcts. In addition, captopril produced greater attenuation of infarct expansion and ventricular enlargement, greater improvement in volume ejection fraction and less decrease in infarct collagen levels than enalapril. CONCLUSIONS On balance, captopril and enalapril attenuated left ventricular remodeling and preserved function in small anterior and inferior infarcts despite differences in the effects of the drugs on individual remodeling variables. Further studies will be needed to determine whether inhibition of infarct collagen might be harmful, or differences between captopril and enalapril therapy important, in large transmural infarctions.