Non-echocardiographic studies in healthy high altitude children have shown right ventricle predominance during infancy and childhood, associated to asymptomatic pulmonary hypertension and an increased pulmonary artery pressure. Systematic studies on echocardiography in such children have not been performed. In a cross-sectional study, we measured right and left heart morphologic and functional parameters, through M-mode, two-dimensional Doppler, and color Doppler echocardiographies, in a population of 321 healthy children ranging in age from 2 months to 19 years and living at high altitude (Tintaya, Peru, 4,100 m). Structured ad-hoc interviews were done to obtain information on medical history, patterns of exposure to high altitude of children and their parents and grandparents, place and altitude of pregnancy and birth, and housing conditions. A complete physical examination was performed before echocardiography. Hemoglobin concentration, pulse oximetry, and anthropometry were measured in all participating children. The right and left heart morphologic and functional echocardiographic measurements expressed by age and by body surface area were generally similar to sea-level reference populations. They were not consistently influenced by sex, nutritional status, chest dimensions, pulse oximetry, hemoglobin concentration, ethnicity, length of residence at high altitude, or parental history of exposure to high altitude. Most children had at least some degree of high-altitude ancestry as assessed by ethnicity and history of parental exposure to altitude. The cardiovascular development at high altitude in children with some degree of high-altitude ancestry seems to follow a pattern similar to sea-level children. The results can be used as reference values to interpret individual echocardiographic studies in comparable children living in similar settings. © 2005 Wiley-Liss, Inc.