In 810 schoolchildren heart auscultation was performed by both a school medical officer (SMO) and a pediatric cardiologist (PC). The prevalence for a grade 1, 2, or 3 vibratory innocent heart murmur (VIHM), a grade 2 or 3 VIHM, and a grade 3 VIHM heard by the PC was 41%, 13%, and 1%, respectively. The SMO noted such murmurs in 26%, 9%, and 1%, respectively. In 30% of the cases in which the PC had noted a grade 2 or 3 VIHM, the SMO agreed; in 30% of such cases the SMO did not hear any heart murmur. If the PC heard a grade 2 or 3 VIHM phonocardiography was performed in a case-control study in which the controls did not have a heart murmur (94 pairs). In four children with a grade 2 or 3 VIHM no heart murmur could be registered and in three other children the murmur did not have the typical diamond shape. In contrast, in three children without a heart murmur at school a VIHM was seen on the phonocardiogram. In 26 children with a phonocardiographically proven grade 2 or 3 VIHM the SMO did not hear any heart murmur. One child with a grade 3 VIHM (both by the PC and SMO) had a minor subvalvular aortic stenosis. There is quite a difference in auscultatory detection of a venous hum: 9% (PC) and 2% (SMO). The prevalence of the pulmonary ejection murmur is identical at 4%. The carotid bruit is heard in 4% (PC) and 2% (SMO).(ABSTRACT TRUNCATED AT 250 WORDS)