According to the anatomical study of the canine heart, abundant collaterals were found existing in the heart. In order to open them up and increase the extracardiac blood flow, coronary sinus was constricted to 3mm. after 1) pericarditis was caused by talc powder, 2) great omentum, and 3) left major pectoralis muscle was sutured to the myo-cardium. The dogs did not survive the ligation of the origin of the anterior descending branch of the left coronary artery. Either single constriction or ligation of the coronary sinus did not protect the heart from ligating the anterior descending branch. Such procedures to prevent the outflow of of the coronary venous blood do not seem to contribute to increase the intercoronary anastomosis. Implantation of the left internal mammary artery into the myocardium will make good anastomosis with the heart muscle as far as it is patent. However, the incidence of thrombosis is considerably high. As dissection of coronary sinus is met with imminent bleeding, an-astomosis is quite difficult to establish complete arterialisation of coronary sinus. The procedure cannot be recommended as a safe operation. The work was supported by grants for the research group of Coronary Circulation and Cardiac surgery from the Scientic Research Fund by the Edu-cation Ministry, 1953, and 1954, respectively.