The effect of polyetox, a medicinal form of high-molecular-weight poly(ethylene oxide) (HMWPEO) on the rheological properties of blood and the necrotic zone size was studied in rats with an acute myocardial ischemia model (on the 5th day after coronary artery occlusion). The drug was infused intravenously in a single daily dose over a period of three days, which resulted in a final HMWPEO concentration of 1 x 10(-6) g/ml in the blood. The first treatment was carried out 1 h after coronary artery occlusion. Animals in the cotrol group with myocardial infarction exhibited high blood viscosity syndrome with stable decrease in the hydrodynamic index. The administration of polyetox reduced blood viscosity, decreased the erythrocyte aggregation, and increased the antiturbulent properties (hydrodynamic index) of the blood. The myocardial infarction zone decreased by 38%, which was manifested in improved EEG parameters.