CORONARY occlusion produces destructive changes in the myocardium, the degree and extent of damage depending on the size of the vessel occluded and the rapidity of obstruction. With sudden blocking of a coronary artery, there is early degeneration of the muscle fibers. According to Mallory and White (7), necrosis occurs within 24 hours. At this time there is an infiltration of polymorphonuclear leukocytes. About the second week there is cessation of leukocytic invasion and an appearance of phagocytes and new blood vessels. In the third week there is laying down of scar tissue, with invasion of fibroblasts and collagen. In the fourth week and thereafter, collagen steadily increases in amount and density and the earlier reaction subsides. In the second month, healing is, as a rule, complete, the site of infarction being marked by fibrous scar-tissue formation. If the obstructed vessel is large, it may result in almost immediate death. The more common type, however, is a gradual, perhaps insidious, narrowing, which produces small progressive degenerative lesions in the heart muscle (Fig. 1). The changes, however, are compatible with life. In these cases, collateral circulation is established so that the heart may continue to function at a lower level of efficiency. This type of case is particularly apt to escape attention of the physician and patient, the symptoms frequently being vague, or suggestive of disease in the gastro-intestinal or biliary tracts. The value of roentgen study in the diagnosis of coronary disease has already been established. The purpose of localization of the area of myocardial infarction tends to serve two functions: (1) it is conducive to more accurate diagnosis which should make possible earlier treatment of the disease; (2) it is of value in those cases selected for operation for the purpose of establishing new circulation to the heart. Wearn (10) writes as follows: “The right coronary artery (Fig. 2-A) arises from the anterior aortic sinus and emerges on the surface of the heart between the right auricle and conus arteriosus (2). Then, lying in the coronary sulcus, it runs to the right and downward where it rounds the acute margin to the diaphragmatic surface of the heart. It continues in the coronary sulcus from right to left to the region of the junction of the auricles and ventricles where it turns to run down the interventricular groove as the posterior branch, and terminates near the apex. In its course, it gives off small branches to the left auricle. Usually, as it rounds the acute margin of the heart, it gives off a large branch called the marginal artery, which, in turn, gives off numerous branches to the right ventricular wall. In its course down the interventricular sulcus, the posterior descending branch gives off many large branches to the right ventricle, to the septum, and to that part of the left ventricle adjoining the septum near the apex.