In 810 schoolchildren (aged 5-14 years) the prevalence of a grade 1-3/6 vibratory innocent heart murmur (VIHM) is 41%. Restricted to a grade 2 or 3 VIHM, the prevalence is 14%, decreasing from 21% in the age-class 5-6 years to 8% for children 13-14 years of age. The prevalence of a grade 3 VIHM is 1%. Together with a matched control, 84 children with a grade 2 or 3 VIHM underwent further cardiologic examination including electrocardiography, phonocardiography, and Doppler echocardiography. A positive correlation was found between the presence of a VIHM and higher left ventricular voltages on the ECG, but within the normal range; lower heart rate; smaller diameter of the ascending aorta (AAO); and higher blood flow velocity and higher maximal acceleration of the blood flow in the LVOT and the AAO. In 40% of the children with a VIHM, a systolic aortic valve vibration was seen with a frequency > or = 100 Hz and an amplitude > or = 1 mm, whereas this type of vibration was present in only one case control. No significant difference was found concerning the prevalence of false tendons in the left ventricle, systolic and diastolic diameter of the left ventricle, systolic time intervals, and shortening fraction of the left ventricle. The VIHM is strongly associated with a smaller AAO, with higher velocity and acceleration of the blood flow in the LVOT and AAO, and with a vibratory phenomenon of the aortic valve, pointing towards the LVOT-aortic valve region as the site of origin of the VIHM.