Administration of a synthetic compound with predicted anti-ischemic and cardioprotective activity, 3,5-dicarbometoxyphenilbiguanide,--to rats with experimental myocardial infarction led to a decrease in the lipid peroxidation level, glutathione peroxidase activity, the level of reduced glutathione, activity of NADP-isocitrate dehydrogenase in the heart and blood serum, and also activity of glucoso-6-phosphate dehydrogenase in heart in comparison with their levels in untreated animals with myocardial infarction. This may be attributed to a decrease of free radical processes and reduction of antioxidant system loading. At the same time the increase glutathione reductase activity observed under these conditions in the heart and and blood serum probably associated with specific influence of 3,5-dicarbometoxyphenilbiguanide on this enzyme.