[Ultrastructural-morphometric characterization of adaptive and compensatory myocardial changes using heart enlargement as an example].

A morphometric analysis of the heart muscle cell shows significant differences in the reaction of different cellular structures in different experimental stress models of the myocardium (swimming exercise and ligature infarction) in the rat. For instance, the number of mitochondria is 44% higher only 2 days after infarction than after 45 h of swimming exercise over a period of 4 weeks. The mitochondria/myofibrils ratio is higher than in the case of training. But later on in the course of the experiment the number of mitochondria and their membrane surface density diminishes compared with training. The differences in the rate of formation and in the kind and intensity of the changes are probably attributable to different adaptive mechanisms by means of which the heart reacts to acute and chronic loads.