Congenital heart diseases are considered in Chapter 21: The Heart: I. Structure & Function; Congenital Diseases. Although the incidence has declined with decreased prevalence of rubella as a result of immunization (Chapter 15: Disorders of Development), other teratogenic factors are continually being identified as placing the fetus at risk. Current incidence of significant congenital heart disease is about 25,000 per year in the United States. The incidence of rheumatic heart disease (Chapter 22: The Heart: II. Endocardium & Cardiac Valves) is also decreasing, in this case due to a general decline in streptococcal infections in developed countries. However, more than 1 million Americans suffer from chronic rheumatic valvular disease. Chronic valvular disease, the use of prosthetic valve replacements, and intravenous drug abuse are associated with infective endocarditis (Chapter 22: The Heart: II. Endocardium & Cardiac Valves), which is the most significant infectious disease of the heart. Primary neoplasms of the heart are rare, with the only common neoplasm the cardiac myxoma (Chapter 22: The Heart: II. Endocardium & Cardiac Valves).