Heart rate during the first five years of life: relation to ethnic group (black or white) and to parental hypertension.

Heart rate was measured in 392 healthy, full-term, appropriate-weight infants and was measured again at 6, 15, 24, 36, 48, and 60 months of age. Heart rate increased from newborn to six months of age and then decreased seriatim. Heart rate did not vary as a function of socioeconomic status or of sex. Blacks had higher heart rates than whites as newborns and at six months of age; at the older ages the difference was no longer significant. The slowing of heart rate with age was greater among blacks. Heart rate was inversely associated with weight and with height, but showed no association with blood pressure. A significant child-mother correlation of heart rate was found at two ages. No significant child-mother correlations of systolic or of diastolic blood pressure were found. Thus, a closer child-parent association was found for heart rate than for blood pressure. Offspring of a parent with a history of hypertension had slower heart rates than offspring neither of whose parents had a history of hypertension. Neither the child's systolic nor diastolic blood pressure varied with the presence or absence of a parental history of hypertension. Results suggest that during the first five years of life a child's slower heart rate may be a better index of risk of adult hypertension than a child's elevated blood pressure.