Two-dimensional and Doppler echocardiography were performed in 70 subjects (aged 1 day to 16 years, body surface area from 0.08 to 2.1 m2) to determine aortic and pulmonary valve areas in normal children and adolescents. Valve areas were determined by the continuity equation using echo-determined ventricular outflow tract diameters and Doppler-determined flow velocities from the outflow tracts and corresponding great arteries. Left ventricular outflow tract diameter ranged from 0.3 to 2.2 cm and right ventricular outflow tract diameter from 0.4 to 2.8 cm. Outflow tract diameters were linearly related to the square root of body surface area. Flow velocity increased from a mean of 0.75 m/s in the left ventricular outflow tract to 1.12 m/s in the aorta and from 0.56 m/s in the right ventricular outflow tract to 0.89 m/s in the pulmonary artery. Flow velocities were unrelated to body size. Valve areas were linearly related to body surface area (r = 0.88 and 0.80 for the aortic and pulmonary valves, respectively). Mean aortic and pulmonary valve area indexes were 1.33 cm2/m2 and 1.70 cm2/m2, respectively. The data provide normal values for echocardiographically determined valve areas and validate the practice of indexing valve area for body surface area.