One of the most controversial problem in cardiac muscle pathology is the existence of myocyte hyperplasia. The term hypertrophy indicates an increase in size of the individual muscle cells without changing their total number, whereas in hyperplasia there occurs proliferation of the myocyte. This fundamental question of the character of cardiac growth remains unresolved in spite of the wide attention it has received. Contemporary views concerning the cardiac muscle hyperplasia are presented. From clinical point of view the problem is significant for two reasons. The loss of the ability of muscle cells to proliferate is responsible for the irreversible myocardial destruction after injury. From another point of view, if the increase of the heart muscle is maintained, although a complete remission of cardiac hypertrophy becomes impossible. In 103 hearts with various forms of cardiac muscle hypertrophy the following parameters were estimated: diameter, length, volume, density and number of myocytes, as well as the density of nuclei of myocytes. The values of all histometric parameters correlated well with the LV weight up to 350 g. In heavier hearts these parameters were approximately at the same magnitude. The number of myocytes was significantly higher in hearts with LV weight above 250 g than in hearts below 250 g: 5.53 x 10(9) vs 4.31 x 10(9), p < 0.001. The influence of coronary artery diameters, degree of atherosclerosis, weight and percent of fibrous tissue and age on LV weight were evaluated as well. From these parameters only coronary artery diameters significantly influenced on LV weight.(ABSTRACT TRUNCATED AT 250 WORDS)