A total of 40 patients with complicated myocardial infarction (MI), with life threatening arrhythmias and congestive heart failure. II-IV degree after Walk's classification, with a concomitant pathology were investigated. Phosphocreatine (PC) therapy (i. v. infusions for 3 days at a total dose of 144 g) made a positive effect on a course of disease. A degree of clinical symptoms of heart failure lessened in 26 patients, disturbed cardiac rhythm got stable in 23 patients. A PC positively inotropic effect was observed. The comparison of the results of PC therapy with those of 173 MI patients on routine therapy showed heart contractility preserved at a higher level and the improvement of gas exchange. A conclusion was made of a favorable effect of the drug on a course of complicated MI.