Per cent fractional shortening of left ventricular internal dimension (%⊿LVD) and mean velocity of circumferential fibre shortening (mean Vcf) were determined by means of echocardiography in 328 healthy Japanese children of school age (179 males and 149 females). %⊿LVD was independent of body surface area and heart rate. Mean Vcf was inversely related to body surface area and directly related to heart rate. These data and relationships obtained were consistent with those obtained from non-Japanese adults and children.