The material of intraoperational biopsies of right ventricle obtained from 54 patients aged 9-40 years with Fallot's tetrad was studied to analyze the changes of cardiomyocyte (CMC) ultrastructure and dimensions in the process of their hypertrophy. The results of the present investigation and the analysis of the literature indicate, that CMC ultrastructural remodeling in course of their hypertrophy follows the pattern of progressive dedefferentiation. Therefore, the loss of the myofibrils at the advanced stages of hypertrophy is not the manifestation of CMC degeneration, but is the result of their relative dedifferentiation. Relative dedifferentiation combines the processes of remodeling of hypertrophied CMC and CMC in a state of chronic hibernation. CMC dedifferentiation in the course of these processes may have a common nature and may reflect the variants of a single general biological phenomenon.