THE FREQUENCIES of heart disease in children of school age are obtained by delineation of a school population at risk of disease. Examinations are performed upon either the whole population or a sample selected from it. Earlier surveys concentrated upon the entity, rheumatic heart disease, a sequela of acute rheumatic fever. This chronic, progressive, life-shortening condition was apparently more common and more severe in western Europe and North America during the early part of this century and the two previous centuries than it is today. Acute rheumatic fever seems to be declining noticeably in severity.70 Rheumatic heart disease mortality rates also seem to have fallen over this same period of time.65 It would be interesting to know whether rheumatic heart disease prevalence rates are lower, too. Unfortunately, direct numerical comparisons cannot be made freely because auscultatory diagnostic criteria have been significantly refined, especially during recent years.72 Improved diagnosis was probably largely due to increasingly successful cardiac surgery, which demanded accurate preoperative diagnosis. As rheumatic fever is becoming less severe, typical cases are fewer. and the diagnosis is probably more difficult in a larger proportion of cases now than in years past. All are familiar with the one-third to one-half of cases of chronic rheumatic heart disease (RHD) which have never experienced an attack of acute rheumatic fever. One may legitimately wonder whether such cases are actually caused by rheumatic fever (undiagnosed or subclinical) or whether a whole spectrum of inflammatory agents can cause endocarditis with valvular deformities. Silber has reported cases of acute and chronic myocarditis with heart murmurs simulating those of RHD, and it is his belief that the label of RHD is too loosely applied in the absence of a positive history of rheumatic stigmata.73 Saphir reports the same phenomena.75 Endocardial elastomyofibrosis occurs predominantly in young adults but has been reported in adolescents and could easily be misdiagnosed as RHD.74 Brucellosis can cause chronic progressive aortic valvular stenosis, although this infection is thought to be rare in children.69 Studies with experimental animals suggest that