Heart diseases, broadly classified into congenital and acquired disorders, constitute a large proportion of illness and death, especially in industrialized countries.
(1) ________ include diseases affecting the pericardium, the myocardium, and the heart valves; disorders involving the coronary arteries; (2) ________ of the pacemaker tissue that regulatesheart contractions; and congestive heart failure. Most heart diseases are associated with inadequate (3) ________ to body tissue or overwork of the cardiac muscle.
(4) ________ implies failure of the foetal heart to develop normally, leading to many mechanical imperfections, some of which are fatal and others of which cause disability. Most (5) ________ of the heart develop during the first trimester of pregnancy. The pregnant woman, for example, may contract an infection, such as measles, have malnutrition, or smoke heavily, all of which may be associated with foetal heart defects.
When congenital defects prevent blood from being pumped normally through the lungs, cyanosis occurs. The infant’s body tissue receives (6) ________, the symptom of which is blue coloration of the skin.
Other congenital defects do not cause (7) ________ but may increase the work the heart must do as a result of ineffectual blood shunting or the obstruction of blood flow. For example, a (8) ________ known as patent ductus arteriosus can occur, in which a small foetal (9) ________ connecting the aorta and the pulmonary artery fails to close after birth. As a result, the lungs receive excessive blood flow, and the heart overworks to pump a limited supply of oxygenated blood to other body tissues.