The importance of microcirculation for disturbances of the blood perfusion of the myocardium is demonstrated by experimental results obtained by the isoproterenol model of rats and the occlusion model of mini pigs. Hypoxia in this region causes very quickly an increase of the extracapillary space and a swelling of the capillary endothelial cells of different degrees. These changes are accompanied by an increase of the ST-region of the epicardial ECG, by a decrease of the myocardial contractility and the coronar-venous oxygen pressure, by an increase of the lactate and pyruvate level in the tissue and a decrease of the creatine-phosphate level in the myocardium. The relation between the wet weight and the dry weight increased in hypoxia, too. The morphological and physiological parameters can be influenced contrarily by infusions with hypertonic mannitol solution. The importance of these changes, especially in the early period of myocardial hypoxia is discussed by the application of the model of Krogh. The necessity of an early influence of these disturbances by pharmacotherapy during the starting period of a myocardial hypoxia is emphasized.