Purchase of this book includes free trial access to www.million-books.com where you can read more than a million books for free. This is an OCR edition with typos. Excerpt from book: CHAPTER IV DISEASES OF THE HEART AND PERICARDIUM MALFORMATION OF THE HEART AND GREAT VESSELS The heart is developed in the first instance as a single tube, with primitive auricle, ventricle, and aortic bulb. The structure later becomes bent upon itself and septa appear in all three divisions, so that eventually there are two auricles, two ventricles, and two vessels—the aorta and pulmonary artery. The commonest congenital malformations of the heart are associated with defects in the formation of these septa. 1. Defective Interauricular Septum.—A degree of this, i.e. slight patency of the foramen ovale, is a very common occurrence (30-50 per cent of cases). In the vast majority of the cases, owing to the smallness of the aperture and to its oblique direction, there is no interference with the function of the organ. In cases of stenosis of the pulmonary artery or aorta, however, the defect in the septum may be marked. 2. Defective Interventricular Septum.—The separation of the ventricle into two begins near the apex. The septum rises towards the base. The last portion to form is the portion represented by the " undefended spot " in thefully developed heart. It is at this point that defects in the septum most commonly occur. As in the case of defective interauricular septum, patency is usually associated with defects in the vessels, most commonly with stenosis of the pulmonary artery. Complete absence of the septum results in the so-called three-chambered heart. 3. Congenital Stenosis of the Pulmonary Artery.— This is one of the commonest congenital defects, and its existence leads to a number of others—defective inter- auricular and interventricular septa and patency of the ductus arteriosus. The narrowing may occur at the valves or in the artery beyond the valv...