The changes of some electrophysiological parameters of heart of the cats in vivo were investigated at the thoraco-and pericardiotomy test. Stimulating electrode were established to the left auricle and ventricle. The electrocardiogram was registered on three indirect and four esophageal leads. During test the electrophysiological parameters such as automatism sinus node; conductivity, refractory period and excitability of a myocardium were defined. It was established, that oppression of

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... sm sinus node, prolongation of the in the auricles, atrioventricular node and ventricles, to increase of a threshold of excitation ventricles results from the thorax and a pericardium opening. The offered method may be used for studying antyarrhythmic drugs, and researches of connections with organoprotective properties.