Last years intensive researches on creation of new prolonged preparations on the basis of natural polymeric carriers with the improved physical and chemical and pharmacological properties have been conducted.One of approaches to the decision of the given problem is inclusion in a matrix of the polymeric carrier known medicinal preparations that will allow purposefully change their properties and activity. Natural polymers, in particular, polysaccharides, unlike synthetic polymers, are biocompatible and do not show collateral toxic effects in a contact with alive organism, and at the same time can improve bioavailability and prolonged action.Carboxymethylcellulose macromolecule (CMC) as the carrier for physiologically active substance has great value, thanking its properties such as non-toxicity, biodegradability and etc.With the purpose of obtaining of the prolonged preparation possessing anti-arrhythmic action, an interaction of Na-CMC with well known anti-arrhythmic preparation of ethacyzin hydrochloride (ETH) is investigated.Na-CMC having various molecular weight, received by hydrolysis of industrial Na-CMC was used as a polymeric carrier. It is shown, that by the variation of time and molar ratio of mineral acid of system during the process of hydrolysis creates possibility of regulation by the molecular characteristics of polymeric matrix of Na-CMC.For the first time, a process of synthesis of with the various contents of medicinal components is investigated at a variation of molecular structure of polymer of carrier Na-CMC.Pharmaco-toxicological studies showed that the polymeric complexes CMC with ETH possess low toxicity in a comparison with ethacyzin, and that, it shows expressed anti-arrhythmic action. An anti-arrhythmic activity of polymeric complex of CMC with ETH is equal to the activity of ETH, but considerably exceeds it on pharmacological properties that prove perspectives of the further researches on it as a prolonged anti-arrhythmic means.