The administration of inosine dosed 25 mg/kg daily during 10 1/2 months prevented the development of excentric cardiac hypertrophy on the background of experimental aortic stenosis in rats, reduced the lowering of the working capacity of the animals, and partially inhibited the full development of functional and morphological myocardial changes, detected by electrocardiographic, vectorcardiographic, microscopic, and electronmicroscopic examinations. Differences were found in the relative weights of the heart, thymus, liver and other organs; these findings attested to an anabolic activity of inosine. The results obtained justify the application of inosine for the prevention of excentric hypertrophy and decompensation of the heart in cardiac failures varying in etiology; any efficient preventive measure is of importance, because the degree of excentric hypertrophy is a factor influencing the survival of the patients.