ACCORDING to statistics taken from some of the large life insurance companies, coronary disease is one of the most common causes of death. Moreover, the incidence of death from coronary disease shows a progressive and actual rise. For example, among the industrial policy holders of the Metropolitan Life Insurance Company, deaths from coronary disease increased 200 per cent in 1933 as compared with 1930 (1, 2). It is, therefore, obvious that every diagnostic aid must be invoked for the earlier recognition of this very common and serious affliction. In a previous communication (3) on the roentgenologic signs of coronary disease we described diagnostic criteria based upon known physiologic and pathologic changes accruing from a multiplicity of laboratory, clinical, and necropsy investigations by a large number of observers. Since then, experience gained in the study of numerous additional cases together with confirmatory observations in other clinics have strengthened the reliability of the signs and yielded additional information useful in the roentgenologic diagnosis and observation of coronary disease. Anatomical and Pathological Considerations The coronary arteries (4) arise from the aorta: the right from the anterior aortic sinus and the left from the posterior aortic sinus (Fig. 1). The right coronary artery runs between the root of the puhnonary artery and the right auricle to the coronary sulcus, in which it passes to the right, giving off an anterior ventricular branch; then, turning round the right border of the heart, is continued on its posterior surface, where it ends by anastomosing with the circumflex branch of the left coronary. The left coronary artery arises from the posterior aortic sinus and runs between the root of the pulmonary artery and the left auricle to the coronary sulcus at the upper end of the interventricular groove, where it divides into two branches: an anterior descending branch, which runs down the interventricular sulcus to the apex supplying both ventricles; a posterior circumflex branch, which turns round the left margin of the heart and continues to its inferior surface, where it ends by anastomosing with the terminal arborizations of the right coronary. The circumflex branch supplies the left margin of the heart and the posterior part of the inferior surface of the left ventricle. The left coronary artery is much more commonly involved than the right (5, 6, 7, 8, 9, 10, 11). Interesting anatomical evidence has been produced by Whitten (10) and Boyd (5), who have both shown that thrombosis of the anterior descending branch most commonly involves the apex and the lower half of the anterior surface of the left ventricle, the anterior part of the interventricular septum and the papillary muscles of the left ventricle. The circumflex branch ranks second in incidence as the site of thrombosis.