Experiments were conducted on 100 dogs with creation of auto venous aorto-coronary shunts in the coronary artery. The hearts were examined 1 year following surgery by routine histological, neurohistological, histochemical and electron-microscopic techniques. No severe destructive changes were revealed in the shunting system. The main processes develop in the heart very early following surgery and consist in reactive changes in the intramural nerve elements, elevation of the phosphatase activity in the walls of the microcirculatory bed, redistribution of acid and neutral mucopolysaccharides and changes of permeability of the haemato-histiocytic barriers; they are an adaptation response of the myocardium to operative stress and new conditions of influx of blood to the cardiac muscle.