Background Myocardial infarction is a public health problem. Functional food is an alternative treatment for cardiovascular diseases. Objective The objective was to analyze the functional and anatomopathological post-myocardial-infarction effects of soybean extract (SE) and isoflavone (IF). Methods Myocardial infarction was induced in adult Wistar rats. After 5 days, an echocardiogram was performed to determine heart rate (HR), ejection fraction (EF), systolic volume (LVESV) and diastolic volume (LVEDV). Animals with ventricular dysfunction (EF n =14), SE ( n =15) and IF ( n =12). The IF group received 120 mg/kg/day isolated IF, and the SE group received 12.52 g/day. After 30 days, a new echocardiogram was performed. A histological exam was carried out to determine the collagen. Activity of biochemical markers [arginase, lactate dehydrogenase (LDH) and malate dehydrogenase] was measured. Results The animals of the control, IF and SE groups showed a reduction in EF after the infarction ( P =.432, P =.017 and P =.320, respectively). An increase of LVESV and LVEDV was observed in all groups ( P =.009, P =.001 and P =.140; and P =.003, P =.008 and P =.205, respectively). A reduction of HR was found in the SE group ( P =.020). There was a greater activity of LDH in the SE group. A smaller quantity of mature collagen was found in the region proximal to the myocardial infarction in the SE group. Conclusion A protective effect in the SE group was observed 30 days after the myocardial infarction.