The investigators documented the nature and extent of changes in cardiac structure based on M-mode measurements and developed corresponding reference values. They documented the nature and extent of changes in cardiac function based on pulse Doppler measures and indices and developed corresponding reference values. They also investigated clinical findings based on M-mode and Doppler measurements as well as changes in body size and composition, sexual maturation, and other covariates. They used existing data from Project HeartBeat! 's 12 four-monthly examinations over the age range from 8 to 17 years.