[Morphology of 2 cardiomyocyte populations in the papillary muscles of the rat heart].

A light optic and quantitative electron microscope investigation has been performed in order to study papillary muscles in the rat heart. Certain quantitative differences have been revealed in the structure of the conducting and working myocardium. Innervation of the papillary muscles has been characterized. A new type of the conducting cardiomyocytes (IV) has been revealed which had not occurred in the composition of the sinuatrial and atrioventricular ganglia of the atrioventricular (His') bundle and its peduncles, their differences from other three types of the conducting cells revealed before are described. The data obtained are compared to morphological characteristics of the papillary cardiac muscles in other mammalian species.