The authors examined the concentration of cAMP in the myocardium of rats with experimental hypertension during various periods after modeling of the process. The changes in the values of cyclic nucleotide corresponded to the dynamics of the development of the arterial hypertension. There was na increase of the level of cAMP in the myocardium on the third day after modeling of hypertension, accompanying the initial elevation of the arterial pressure. The maximal values of cAMP were established on the 30th day, which corresponded to the maximal development of hypertension. Cyclic 3,5-adenomonophosphate began to diminish parallel to the lowering of the arterial pressure during the chronic phase 90th day. The obtained results give a possibility to discuss the participation of cAMP in the pathogenesis of myocardial hypertension, occurring in experimental hypertension.