Serotonin is a monoamine neurotransmitter and hormone that exerts its various actions by binding to the receptor membrane in cells. 5-HT2B receptors are actively involved in embryonic morphogenesis and regulate the development of the heart. 5-HT4 and 5-HT2B are involved in myocardial contractility and affect the temporal parameters of regulation. One of the main mechanisms controlling cardiac activity is also connected with the effect of catecholamines on adrenergic receptors of cardiomyocytes, which mediate the action of the sympathetic nervous system, being the main factor contributing to multiple changes in the development of myocardial cell function. In the given study, there is reliable data provided to indicate that the effect of different concentrations of adrenaline leads to a decrease in contractility of the right ventricular myocardium in 7-day-old and 14-day-old rat pups with an altered serotonin concentration, which was created by a blockade of the synthesis of serotonin and the membrane serotonin transporter in the embryonic period of ontogenesis. The total duration of myocardial contraction is decreased in experimental groups of animals. Thus, the smallest decrease in the time of contraction and relaxation in comparison with other groups is observed in 7-day-old rat pups with an excess of serotonin; in 14-day-old rat pups with a lack of serotonin. Thus, a change in the concentration of serotonin in prenatal ontogenesis can possibly affect the sensitivity of adrenergic receptors in postnatal ontogenesis.