An effect of different interventions on the electron microscopic structure and morphometric parameters of the myocardium were studied. Application of cyclophosphamide and isoprenaline in the experimental animals allows the similar changes of mitochondrial partial volume like hypoxic periods of cardiac surgery by coronary bypass operation. Although the initial agents are different, the primary affected structures are sarcoplasm and mitochondria, whose proportions change promptly. The primary effect may be connected with alteration of membrane permeability caused by increased osmotic active ion transport on responsibility of the inhibited Na, K-ATP-ases (or F0 F1-ATP-ases irreversibly altered in mitochondria). The morphometric evaluation confirms not only statistically significant differences among the experimental groups treated by cyclophosphamide, isoprenaline and by cardioplegic ischaemic periods in the human myocardium but also by application of physiological saline in the control groups. Comparing the morphometric evaluation by manual processing with computer mediated image analysis we can conclude that the results correspond upon conditions of the specific defined raster for Weibel's intersection test only.