The effect of the nucleoside Inosie-F (inosin) on the intracardiac hemodynamics and the contraction and relaxation of a diseased myocardium was studied in the clinic and in experiments. An examination was made of 102 patients with macrofocal myocardial infarction (22 received inosin by intravenous drip in a single dose of 200 mg in the acute stage of infarction; 60 patients were given inosin pills in a daily dose of 800 mg in the restoration period for one month, and 20 patients were given placebo). Comparative appraisal of treatment in the period of rehabilitation showed prevailing improvement in the condition of individuals treated with inosin, positive ECG dynamics, increase of cardiac output and decrease of peripheral resistance. In experiments on 28 dogs with a model of acute myocardial ischemia a noticeable improvement in myocardial contraction and relaxation in the absence of negative ECG dynamics was recorded after intravenous infusion of inosin. Inosin achieves maximum effect by 60-90 mins after the beginning of infusion.