Heparin administered at the initial stage of myocardium infarction is shown to prevent a number of shifts in the metabolism of protein and polynucleotides of the injured heart. It does not promote the development of some changes, but intensifies only a few of those evoked by the ligation of coronary artery in the myocardium nitrogen metabolism. The preparation inhibitory effects are also slightly pronounced in the normal myocardium where the preparation activates many metabolic reactions of nitrogen-containing biopolymers. Inactivation of enzymatic systems in a cell is likely to be not the basic, as some researchers consider, but one of the secondary mechanisms of heparin incorporation into metabolism proceeding in normal and pathologically changed tissues.